Sculpting wrinkles

Two questions
Im trying to find a way to achieve the kind of look of this picture with sculpt cloth brush. The idea is get that inflate look with tension wrinkles at the borders

The other question is about the scale of the wrinkles. When Im working with cloth brush in sculpt mode, how can I change the size os the wrinkles?. For example, I want a look of fine details for a bag or maybe a larger wrinkles for a bed sheet, what I need to tweak for this? Less polygons, scale of the object, any parameter in the brush options?

Thanks in advance