surely a level on the gg head will make that obvious. I think the pots need to be flipped before trimming hardness arrives. Rim will be drying way faster htan the foot which if recaught on bat will lead to warping.
Being level - and being centered are two different things. It's possible for the GG to be perfectly level, and still not be centered on the wheel-head.
Try using a pencil or piece of chalk (instead of a needle-tool) to check both the wheel-head and the GG to make sure they are centered and round. (This will leave a mark on the 'high' spots if there are any, and make it easier for you to see where it's off.)