I just checked the seats on my three bricks. The gap between the tank and the front of the seat on all of them is at least a quarter inch, and closer to 5/16". The front of the seat has never been close to the tank on any of the 5 bricks I've owned. Your photo doesn't look unusual to me.
As far as sitting low and hitting the battery covers, is it on both sides, or just one side? Is it the hinge side? Can you post a photo of the bumpers on your seat?
I don't have a Corbin seat here anymore, but I think you can use the OEM bumpers which come in two versions. One is about 3mm thick, or a bit less than 1/8" and the other is closer to 1/4", maybe 5mm.