I would try blocking it off as you mention. As long as an ammonia refrigerator can vent it’s heat out of the top it will work. One of mine would not keep the refrigerator cold when the A C was on. I finally figured out the AC was venting its heat directly over the refrigerator vent. I blocked off that side of the AC vent and it works fine.
Those limitations on being out of level are for stationary operation. Going down the road , uphills, around curves, it’s no problem.
