I was testing some late season lures last year and I had a hollow log that was 14-16 inch diameter I place the lure inside… red fox, grey fox, fisher and coyotes had no problem working the log even though they couldn’t see over it… i have tons of video showing this…. So does backing height really matter or that important?

Grey fox, it makes zero difference. For coyotes, the higher the backing, the farther from the backing your trap needs to be. Can't speak to the other varmints.

Yup, for coyotes is certainly does as Lazarus stated and I also have plenty of testing videos that substantiate that fact. If a softball-size clump of bunch grass is used the coyotes will step up close and then step over the clump and straddle it!

My most successful coyote sets have been up against backing at least 18 inches tall, sometimes more. I am not as experienced as many on here, but I haven't noticed tall backing being a problem. Short backings make it hard ( at least around here ) to predict where a coyote's going to step.

The wives tale that a coyote won't work a set with a large backing is a wives tale. Watch JC Conner's trapping videos.

I don't have a lot of experience I usually try to have as small as can get away with and not have them dig from the back side.it verys for me I've got away with rocks smaller than a baseball to a knot as big as a basketball.

Can you catch some coyotes with tall backing? Yes. Are there coyotes that tall backing makes them more nervous therefore harder to catch? Yes.

I've caught lots of coyotes on vertical field road cuts that were five to 20+ feet high and the set right tight to the base of the cut. I think, however, they are not as nervous at extremely tall backings like a vertical road cut as they are at a backing they can almost see over. Just my observation FWIW.

Agreed. When I set against a backing /Grass I try to trim any over hanging grass with scissors vertically ,.I don't trim it hard back but enough that if a coyote works the set the grass will not be hitting his face,.No issues so far.