They do seem to prefer the flat filters!
I'm wondering why?
Given all of the other nesting...opportunities available in my garage, what is so appealing about the filter of a cold hunk of metal sitting motionless over the winter?
One year, there was an affinity for the bell housing of my F-150; two clutches in as many months!
Not quite as cute as Beverly Cleary portrayed them.
Thus far, the 1/4" has repelled them; also effective against flying squirrels invading the attic!
Opinions are like internet connections- everybody has one.