Yes, the bigger the size, the wider the calf. If you want to be sure of the circumference for a particular size, I think it's best to e-mail or call the retailer/boot maker.
I have seen the site you mention but never used it. I was wary of ordering boots from there because I thought, What happens if the boots themselves (not even considering the calf) are uncomfortable, or what if the shaft is too high, or what if the sizes run large/small and the boots don't fit in the foot? Then the company will alter the calf on a boot that I don't want, and I assume that my money will not be refundable then. But I didn't read their policies, so I don't know how they avoid this situation. Maybe they send you the unaltered boots first so that you can pick, and then you'd have to return them for the alts. I would just check this kind of thing out before ordering.
