What is the maximum angle I can set my window AC unit?
All the window air conditioning units I have looked at&mdash;a total of about six different models&mdash;had a drip basin which is tilted toward the outside.  Or if they have a drain hose, then the pan is tilted toward an exterior corner where the hose nipple is.

So leveling the bottom of the a/c should be the right thing to do.  If it is tilted too far, that could cause water to accumulate in the wrong place and interfere with the condenser, or maybe just overflow onto the sill bypassing the drainage system altogether.