I just set mine on a shelf near the TV and it’s been fine. I never bothered trying to mount it high up, so I’m not totally sure if it would make a big difference. Maybe it depends on your building or something.
I think you’re overthinking it honestly. I put mine under a pretty bulky case and haven’t noticed anything different, so I’d say you’re fine either way. It’s just a sticker, not like it needs direct contact with the air or anything. Probably works the same.
I think it’s probably more of a deterrent than a full solution. I used them in my RV and didn’t notice any problems, but I also wasn’t exactly watching for mouse activity either.