I would not worry about a little difference in oil height. If you were way off it might affect the air spring, but only near full compression and would have not noticeable affect in everyday riding. Most certainly could be a bad bushing.
A friend dropped off a set of forks last week to get looked at. He had issues last year at a trackway where the forks were harsh and he was not getting smooth operation. Sticky feeling, hard to compress were his comments. I said I would take them apart and have a look for him.
After about 20 seconds I knew I would see something interesting when I got them apart.
Here is a short clip I took before disassembly. The only way to describe them was disgusting.
Turned out to be only one bad bushing. The bushing pressed into the outer was fine, the slider/bushing on the chrome tube was a disaster. Lots of deep gouges and the amount of bushing material that came out with the oil was massive.
I am also pretty sure they had been filled with engine oil, not fork oil. It was an ugly set of forks.
Pick up some bushings and strip them down if in doubt.