I run into this often as my dress carry belts are half the width of my normal, every day carry belt. But honestly I've never thought twice about it. My holsters still sit snugly where they are intended to be.
In fact, ALL of my holsters would be too big for my belts if I didn't usually wear a 1.5-inch Galco belt... it fills up everything.
If it really bugs you, try folding up a piece of leather or suede around that part of your belt and see if it snugs it up for you?