Windfall, yes the photo is one of my shells over a full sized hive. No I’m not intentionally letting bees get between the wood hive and the shell. What happened here was my wood top cover warped on me (made out of luaun) and generated a gap from which the bees could exit the wood hive and get into the foam shell. From there, they proceeded to chew!
In general I haven’t noticed a desire for bees to chew foam in my numerous experiments; unless they feel trapped. I have seen them chew at the foam in the bottom of a feeder once the feed is consumed.