The size and shape of the belt is an unknown in the breed. The belt itself is exceedingly strong, regardless of shape or width. The thing is, it is unclear if the belt trait is really a homo or heterozygous deal.
I have a purebred heifer out of purebred belted parents that came out pure black. The cow throws a black calf every other year despite purebred parentage for many generations(at least 5 on the pedigree).
This heifer will have purebred belted calves when mated to a pb bull. I expect them to be properly marked.
As I mentioned earlier, a sale barn is a bad place to take niche cattle. If you see some there (that aren't mini stock) you better buy them. Heifers are high and steers make excellent table fair.
If it was easier to post pix on this site I would gladly share images of beltie cross cattle and their beef products that I sell.