Been caught a couple of times with uneven ground after refueling. tell tale sign was the blue stain on wing and flap.
Mostly not possible to refuel before early takeoff.
I replaced the O rings under the vents to give me a couple of inches leeway but still overflows on uneven ground.
I guess that the fuel heats up and expands and coupled with the slopes encounted causes the problem.
I now only fill to the tabs, probably only 5-6 lts a tank unless I need the extra for longer legs.
I used to have a 230 home built that had a tap for each tank, turning off stopped the cross feed problems. The factory built has no wing tank taps, just a main on off tap. Much better for safety I reckon but you must have even ground.
Phil