I've gotten blisters there before with two pairs of boots. I had to return a pair of boots because they were just too painful. I think this is fairly common, because it is hard to generalize the shape of the heal. I once had a problem with a pair of boots that I thought would be perfect for me. I needed a pair of boots for the Spring, when hiking in the snow (my feet get wet if I'm kicking steps in slush). I found a pair that was supposed to be really soft and fairly light, but still a mid top with all leather (and thus waterproof). This was perfect for me, because I have strong ankles, and don't need the extra support that many boots provide. Unfortunately, they tore up my heals. I visited Dave Page, the cobbler (who works on hiking boots quite a bit) and he told me the problem. The Vibram sole was stiff, but the rest of the boot was not. When I hiked up a steep trail and bent my foot forward, the back of the boot stayed straight, while my foot slipped in and out of the heal, thus causing the blisters. The answer was to either get a stiffer boot (which I use in the Spring) or get a boot with a more flexible sole. The stiffer boot grabs my foot more aggressively, and thus I can't bend my foot as much (and my heal doesn't slip out) while a softer boot (a trail runner) is so flexible that the entire thing moves with the foot.
Hi-Tec changed their style over the last few years (it may be the last ten years now). They used to make very simple, very soft boots (essentially trail runners, but some with a mid-top and many with a more aggressive tread). They used to fit and feel like sneakers. Now, they are much stiffer. It may be that they are a bad combination (I've tried on several in the store and I didn't like them).
I also have to add that unfortunately, if you are like me, finding comfortable boots may not be easy. My story about the soft, full leather boots is a good one, but I also had a big problem with a pair of trail runners. The only thing I can suggest is to try on more shoes, especially trail runners. Step on a slanted surface (if it exists in the store) and make sure your heal doesn't come out of the boot. Also check the heal area to make sure there are no seams or other parts that might cause a blister (you haven't had any, but if your heal is being beaten up, then a blister could easily occur with a similar boot).
I might also add that I agree with Dan: your are much more likely to find a comfortable pair of trail runners than you are a comfortable pair of heavy boots.