I was thinking of checking my transmission fluid levels, but then I realized something when I went to level out the car.

[Looking from the passenger's side fender]
The top of the valve cover and the bottom of the transmission are not parallel (or level). If I try use the top of the valve cover to level out the car, the bottom line of the transmission angles upward. If I use the bottom line of the transmission, the top of the valve cover angles downward.

Which one should I use as my level for making sure that my tranny fluid is filled optimally?