Most tanks will have some movement on the bowl. After installing hundreds, we realize that whether the tank does move or does not move, it's all pretty much the same.
If you "need" a tank that "does not" move, I would suggest one of the one-piece versions like the Ultramax.
You pull the toilet out of the box and stick it on the wax. It's a very nice way to go.
We install hundreds of these tanks and have never broken one.
I wouldn't worry if there is some movement. Check these Instructions