I have 18"-19" calves (yes, one leg is wider than the other; I'm lopsided ;) and pretty stocky legs, so here's my take on the fit.
For the scrunch boots: They were pretty snug at the top when I first tried them on, but after a day of wear, they zipped up just fine the second time. My feet/legs were a little sore after breaking in the first pair, but I think that was more due to me not being used to wearing heels (I'm a flip-flop girl in FL) because the second pair I broke in didn't leave my feet/legs sore at all and they were the exact same boot.
I'm breaking in the stretch suede ones today, and I have to say these are my favorite of the two styles. No problem zipping them up, even right out of the box, so I think someone with 20" calves could do these ones, too. Because they're stretch, the ankle doesn't feel as stiff as with the other style (and I like that - if you need ankle support in heels, these probably aren't the boots for you). Also, I think the suede stretch ones look sexier because the heel is slimmer, but they actually feel like a lower heel and look a bit pirate-y with pants, which I LOVE!
I'm still thinking about getting LB's third style now that they have my size in stock because I think the slimmer line would look better with skirts than the scrunch ones, but I got such a good deal with my first order and I'm a bit hesitant to spend $60 on a pair of extra boots. With the outerwear sale that they had going on when I bought mine combined with the coupon I used (spend $150 get $50 off, which you can find here), I got my original three pairs for around $30 each.
So, if you're looking for some fall boots with a heel, I would definitely recommend you grab a pair of these. They're good quality for the price (unlike LB's clothing nowadays IMO), and they feel pretty sturdy under my 270 lb. frame.