Bryan As long as you can't shimmy the belt over the hip bones it's not coming off! The curves of a corset should mimic the natural curves of the body. The belt doesn't have to be too much looser, maybe a single pant size at most. Most belts have that amount of adjustability built in to account for bloating etc. If anything the waist band would sit ever so slightly higher, meaning the shield / crotch section of the belt is pulled closer to the body (making it tighter).
In most cases the corset is far more restrictive than the belt. I have a steel boned PVC waspie, a very restrictive latex overbust and a few fancy bridal lace types. Only the bridal ones have clasps in front. The kink ones aren't exactly designed to escape from! The fitted shapewear I use is like a corset-shaped singlet, I use it specifically to stop the belt chafing. It's really only the thickness of a T shirt so I don't have to resize the belt or anything drastic.
If you're getting a belt made I would suggest an anatomical hip band if you want your corsets to last. Steel is very unforgiving.
