Can we maybe talk in height and weight (preferably in SI units) rather than dress sizes, which
a) mean nothing to me
b) seem to be different anyhow depending on where you are from?
At some point I would assume a belt would not work anymore. The hip bones prevent the belt from simply being pushed down. If waist belt is larger than hip, it would probably be possible to slide the belt off with some effort.
Security might be compromised anyhow because a thick fat layer under the skin might allow for fingers to reach the forbidden zone. The only way to prevent that would be to make the belt extremely tight which then would cause all sorts of skin problems.