I am having the same issue right now. Without the rubber ring, the tank sits perfectly on all three points. When I put the ring on, the gap between the tank and toilet bowl is about 3/4"
When I snugged it down, I was able to get it within a hair, but honestly I was paranoid I was going to crack one or the other. Something seems off. I know we shouldn't have to be tightening these down this tight.
See my pics:
No ring.. it sits flush
Here's where the ring sits and the height it absorbs
What I assume is the ring, correctly attached to the fixture
This is the height of the tank, just sitting on the bowl. Is this really the height it's supposed to be?
piezomot, are your issues similar?