There were problems with the original fuel sending unit in the sixth generation Accord. My first one went bad about six months after I had the car. Same kind of problem you described. Fill up and only see 3/4 of a tank. Dealership replaced the first one and it happened again. The next time they admitted there was a design flaw and told me to wait because a redesign was in the works. It took two more sending units but the last one I got has lasted for about 2.5 years.

I doubt if it is a ground problem. All of my problems were associated with the unit itself. All of mine were covered under warranty.

If your car is out of warranty, the unit can be accessed through a cover plate in the trunk. Never had to replace one myself, so that's about all I can tell you. Good luck.