It's entirely possible that I'm a grumpy old man. I just went through my last chemo treatment ( for the foreseeable future) and I'm in that weird phase where I crave spicey foods but have a sensitive gut. I need to go buy some halepeno sausage, but I will probably regret it later.
So that's my excuse for the Carley Simon impersonation.

If I cover with dirt, I'll use a brown coffee filter
In frozen ground, I like a clump of green grass under the pan because I'm typically setting between 2 large grass clumps

After trying everything over the years including Zaggers method, I now use nothing but polyfill under the pan and bed and cover with wax dirt and blend in. Don't do much landtrapping anymore except to fill my Fisher tags since you can't hardly give away a coyote pelt from around here anymore.

I haven't experienced anything negative with poly fill, although I don't usually use anything. Only thing I noticed is it's best to keep it small and all under the pan.

I don't know but 100% Egyptian cotton sheets or those new stretchy Sheeks pan covers are all the choice of the Real Trappers of New Jersey I've heard, lol. I'm a pipe insulation fan.

Wax paper here. Every dirt set.

I've used wax paper too, works fine

Straight peat, no pan cover needed.

I think that the problem is our rodent population. When I tried wax paper, squirrels and chipmunks would uncover it. Not that they don't play in the dirt regardless, but it's less of a problem without pan covers.

Poly for me , here is about $2.00 of quilt batting from the craft store. Some animals destroy them but they are cheap, never have had mice problems like I did with landscape cloth pan covers.



wws

Ball of Poly under the pan. Just enough to let me hard pack around the pan without impeding it triggering. We have pretty packable dirt around me, so I don't have to worry about it coming out from under the pan and looking frizzy. Only thing I don't like it is seems to hold moisture under the pan and makes the rusting worse. Obviuosly this is only an issue after resetting after a catch and some of the wax has worn off.

Hate pan covers. I went with rubber foam underalls 3 yrs ago and never looked back.

I use pan covers and nothing under the pan. I used just about every under pan thing for decades and best I found was nothing under the pan, period.
I used to use things like polyfill, pipe wrap insulation, underalls, most of stuff. Even dipped them in something to waterproof and squeezed fluid back out then dried. I will NEVER put anything under my trap pans on winter coyote line again.
Stuff under pan here will not work in a light right or freeze thaw in our late winter coyote work, period. Works sometimes, but not reliable. Works early in season, but not hard freezes later. Anything porous I put under the pan held water like a sponge and in deep winter here froze solid like a rock and pan could never move down enough to fire the trap. That’s polyfill, pipe wrap, or those foam under all thingys. I read stuff on here all the time and have for years. And I’ve gave a lot of a fair shake try too. Believe me, i’ve tried it all. For stuff under the pan.
Best thing I’ve used so far is: layer of waxed dirt in bottom of trap bed, then bed trap in that, make sure nothing under the pan, use a pan cover like fine screen or waxed paper, then a thin layer of waxed dirt over trap. Waxed paper works better than screen covers but screen its a close second. Waxed dirt below, space under pan, cover over pan to keep top layer from working down under the pan, and waxed dirt above to cover. Don’t “blend” with anything like surround soil or it will be a hard crust. Just waxed dirt only to top it off.
That’s my take. I’m talking when we hit the sub zero overnights here for many nights and after a few days we get freeze thaw or freezing rain or snow. This has hands down meant more operable traps for me in coyote line than any other method I’ve used.
Peat will freeze a crust, so will cover hulls. Waxed dirt period is best I’ve used.
I’ve had to rebed so many traps over the years with something under the pan that didn’t fire. Made me sick how much time and resources I wasted and couldn’t catch set visitors.
Jim

I agree with PAskinner,if your trap is ready to fire with little movement. why use covers. I strted out trying to use covers and gave them up long ago.

Again, as it has been explained to me, the theory of the steel screen covers is that they are rigid and therefore "extend" the pan trigger area, which in theory will trigger if the animal steps anywhere within the jaws, not just on the pan.

How well that works in reality, I can't say since I lack the experience. Does the increased area result in enough additional catches to make it worth the trouble?

The answer is yes

Steel screen expands pan, resulting in more catch’s

I roll up a leaf of corn husk off of the ear and push it under the pan the wax on the leaves keeps it from freezing ,Its natural and costs nothing . The pan only moves a small distance so really pan covers are over kill

Cool

The screen wasn’t used to increase pan area, it was used in areas with high precipitation. Down here we may get 2-5” of rain a week or all at one time. And if you get it all at one time, 12-24hr time frame, then your sets are pretty much washed out. The “Pipe Dream Set” isn’t the pipe or the screen. It’s all in the way it’s bedded. Deep concave hole with levers holding it in place. Get a downpour and hole fills up, screen on top with some grass/duff/leaf and your trap is still functional. And yes, it works. If my 2 week forecast shows a lot of rain, one set will be the traditional and the other across from it will have a screen cover bedded the Pipe Dream Set way.
Normal (traditional) sets get polyfill underneath the pan and does a great job as keeping dirt from getting under the pan during downpours, it’s just generally the trap gets exposed. In fact it works so well, I just use dirt I carry to add some dirt over it. It’ll still fire, but a coyote ain’t known for stepping on exposed sets.

So here's my follow-up question:
If a steel screen increases the trigger area, doesn't that also increase the chances of a toe-catch (or even a miss)? The benefit, I think, of making the animal actually step on the pan for the trigger would seem to be a higher chance of a full-pad catch. But if the animal steps near the edge of the jaws and the trap triggers, I would think that would result in a lower chance at a full pad catch.

So, if the steel screen does result in a higher chance at a catch due to the increased trigger area, how much of that is balanced by undesirable toe catches or even misses/escapes?

(And I see that Wanna Be disagreed with the theory of the increased trigger area, but I've heard enough trappers advocate it that I think there's at least something to it; I'm just curious how effective it actually is.)