The hole just needs to be no bigger than that, so sounds like you can just leave it the way it is. The hole especially can't be too wide but could be taller a bit as the metal would cover the top part of a tall opening.
We just had the same dilemma here...our 8 five-week chicks, had only put themselves to bed for the first time the night before we were to leave for four days. My Ador was on its way at that time and I didn't have a sitter, so we took them with us! They traveled in a dog crate and slept there at night. During the day the hung out in a 6'x6' dog kennel with chicken wire around the bottom and plywood on top. It worked out okay but boy were they thrilled when we got back home last night and I let them loose in their 20'x16' run! They ran around making noise and ran in and out of the big coop like kids on Christmas Morning.
I have one installed in the door to my shop. I slam the door sometimes and it goes "clang". Not recommended to bang it around of course but my advice is to not forget that you should operate the human door smoothly...no slamming. Slamming hasn't broken mine yet but I don't slam on purpose and not that hard. One of the more likely hazards of mounting ADOR tilted or where it vibrates or moves is that the battery terminals might electrically touch against the printed circuit board, causing a short circuit. That could kill the electronics. The insulation around the alligator clips makes that pretty unlikely but you could slip a 2.5" x 2.5" square of corrugated cardboard between the battery and the back of the electronic board. I think it is pretty low risk to mount ADOR on a human door that is only used for you to access infrequently the inside of the coop.
