AS has had some QA/QC issues, but if yours is 'good', it should work. Course, that doesn't help much! FWIW, unless you have less than normal strength, setting a toilet is not difficult. On a two-piece, if you set the bowl, then add the tank, it's quite a bit lighter, but then you have to crawl around under to tighten the tank up. It's not a big deal, but a consideration. Most plumbers would attach the tank, then set the whole thing.
It's possible that when the plumber set the toilet, the wax ring (or if he used a wax ring with an internal funnel), the wax or funnel have closed up part of the opening. So, the toilet could be fine, just less than stellar installation.
Unfortunately, the only way to tell if that's the issue, is to remove it and look.