Refusals have never been an issue with any of the cages. If they won't go into a cage of one size, they won't go into any cage. Either they will or they won't regardless of size.
I have not found this to be accurate for me. The larger the opening, usually the easier it is to get the animal into the cage. Especially when the trap is on land. The width of the trap in relation to the height and what type of trigger used with the type of set is also very important as to the number of places the trap may be used most effectively at a location. Even the door type and how fast it closes is also very important.
A short (32")guillotine powered double doored (long spring) trap that is at least 14" wide and has a set door height of at least 16" has been proven to me to be the best beaver cage trap I have ever used. That size makes the approaching beaver feel less wary. The 12" tall lock bar designs work but limit set locations more so than a guillotine doored trap. Sometimes it is best to use one design over another simply because of a particular situation. One would never know unless they have used what I have described.
The easiest set to me is two 14x16x32 powered door guillotine doored traps using a conibear trigger, set side by side in 4 to 6" of water. Place grass between them and place lure on grass. Often you will catch two. If the stream current is fast and you are setting a stream, bend wires up or make the set perpindictular to the stream current. One can even hang lure on trigger depending on type of set.
Another very effective set is a dog sized powered door, side door trap set in 6 to 8" of water on a level area in a pond. Preferably near a cross over or active dam. Just place lure on clump of grass in trap above trigger like a koro.
A koro beaver trap is a very good trap also because it appears most open, but it is limited to baited sets.
So what is needed is trap variety to cover the most situations.