Technically the lower the COG better but in reality you’ll never notice the difference raising the camper 2”.
I like at least a few inches between the cab and cabover because trucks and campers flex.
I’ve been doing the 2” thick 4x8 sheet of rigid foam insulation thing for years now.
Yeah it’s one more thing to do and I’ve worked to eliminate loading hassle as much as possible, but they really weigh nothing and you just drop it in. I may end up glueing it to the bottom of the camper but I do anticipate replacing the foam at some point so I kinda don’t wanna glue it on.