Yeah, I'm with TG and Jonesy: I don't think it's a big deal if there is a bit of a gap at the top of the boot. Nothing extreme, but an inch or so doesn't bother me. And as someone with large calves, I have to admit that I actually *like* the look of a little bit of a gap. It makes me envious.
Boots are difficult to get perfect, and unless we are among the few who are blessed with average calf circumference and average shaft height, I think compromises are sometimes made. I have 15.5 inch calves but am otherwise quite small (with small ankles), the distance between my ankle and knee is short, AND I only buy vegan shoes. When I found a pair of really cool, grey, vegan boots that fit my calf, did I not buy them because the shaft was an inch or so too high? No, I bought them anyway. It was that, or no boots at all.