OK, OK, the Champion is the "worse toilet" out there, but...
As you have noticed, there are many respondents who detest the Champion toilet, much less anything manufactured by American Standard. Some of that animosity is deserved but, like you, I found the Champion to be extremely clog-resistant, which was a huge plus in this household. Once I got past the pesky piston flush valve (replaced with the new-and-improved flapper type), I am completely happy with the Champion.
But, yes, the Champion tank does not always sit squarely onto the bowl. I have two Champions: one sits nice and straight while the other is slightly skewed forward to the right. Both DO NOT touch the back two nipples, supports, or whatever you might name them, on the bowl. Yes, the tank may lean slightly to the front of the toilet. In my case, I don't notice it since there are walls surrounding both toilets. Even with the perfectionist-foiling (yep, I am one of those perfectionists...) tank-to-bowl hookup, I have no leaks and a seamless operation of the toilets. Sounds like you have the same scenario. Thus, I wouldn't worry about it unless it really bugs you...then you can try re-seating the tank to the bowl and hope for better results--good luck!