I sand all my backs and always have. I use a sanding block on the belly to knock off the last 3-5# and rid it of any wash board ripples, same with the fades. I just cant stand rippled fades! Gotta be a smooooove ramp.
I go all OCD on that same issue. Drives me batcrap crazy, can't sleep for weeks, teeth sweating, coffee cup jittery, snapping at old ladies in line at the grocery store, mean and ornery.
Always wondered if that was just my special burden!