hey, I would be totally shocked if that were the case, in fact that would probably make them want you more, not less 🙂
Also, the previous poster is correct, they don't have any way of knowing that until the schools share lists. The party line at UB is that the waitlist positions are set in stone, except they reserve the right to pick and choose as they get down to the wire. But "the wire" is early August. I would say with pretty much certainty that until then, they just go down the list and accept according to position. If you have time on your hands and want to check out last year's thread you can see when we got to your position (bottom of top 1/3, I think you said?). Off the top of my head, I would guess that we got there sometime in late May, but you can check that out. Your chances are excellent. I was in the middle of middle and I got accepted in mid-June.
(edit) okay, procrastinating here, I checked last years thread and we entered the upper portion of the middle 1/3 on May 23, which means we ran through an entire 1/3 of the waitlist in about a month. Getting through the next 1/3 happened much more slowly...