I'm so sorry you are not loving your boots!
I'm not an expert, but I do have large calves as well so I struggle with the whole tall boot thing every year. I think that probably most leather boots are going to fit this way, with a little gap. If they are large enough to fit the calf, they will most likely gape a little bit at the top. I just think it's a function of the calf size, more than the boot.
Personally, the little gap doesn't bother me, especially with jeans tucked it. I think you look great in your pictures.
However, if it bothers you maybe you can look for a boot that is made from that stretchy synthetic material, or perhaps one that has an elastic gore down the back? I've seen some like that on Zappos, in the "extended calf boot" section. Stacy London always touts those boots as great for larger calf women. I'm not in love with the look of those types of boots, so I have never bought them, but I can see how they might grip the leg differently.
Also - depending on how long your legs are, you might want to look for boots that are slightly shorter in shaft height, so that they end just at the top of your calf instead of higher on your leg. The boots I bought at Eddie Bauer last year have a shaft height of only about 13". When I wear them with tights I don't really get as much of a gap. The boots I bought this year from Rockport have a shaft height of 15", so they come up higher and there is a gap. But I love the look of my new boots, so it doesn't bother me at all.
Again, I understand what a personal issue this is so I really hope you find boots you love!
Perhaps Angie has had experience with large-calf gals and boots and she'll weigh in on the matter.