Don't trust those straps/belts to hold the bags in place, they WILL loosen up, that style of buckle looks like it would wedge the belt but in reality it doesn't work all that well.
Yeah I know they are the pits. They remind me of the belts we had to wear in Boy Scouts (man, that was a LONG time ago) and they were pretty useless. I got them because they are tan canvas and I like the look (and they were cheap). But they will need something to make them work right. Some velcro pads sewn in as is being suggested might be a good idea.