My belt also rides up in the back when I sit, which is why I take it off when I drive. Anyway, I've found solution that works most of the time... I just sit up straighter. It seems to work for me anyway.

Another thing.. about the belly button being below the natural waist. My belly button is covered by the bottom of my 2"-wide belt when I wear it at my natural waist. Maybe it's because there is less than 3" between the top of my pelvis to the bottom of my rib cage. Just saying.