Placement of indoor minisplit unit

I am about to have a Mitsubishi minisplit installed. In case it matters, the installation will be on an interior wall; on the other side of that wall is a closet with a sump pump which we will use for drainage.

The unit (#MSZFS12NAU1) is 12.6 inches tall and 9.2 inches deep. It will be installed above a 9" deep bookshelf. The distance from the top of the bookshelf to the ceiling is 19.25".

The contractor says that distance should be at least 22", so the bookshelf has to go and be replaced by something shorter. I am inclined to try the experiement of keeping the existing bookshelf, living for a while with the minisplit, and then replacing the bookshelf if (and only if) I am unhappy with the performance.

Question 1: How likely is it that the difference between 19.25" and 22" will significantly affect performance?

Question 2: If performance is in fact affected, can I compensate by changing the temperature setting? For example, if I would normally set the temperature to 70 degrees, but the performance is hampered by the proximity of the bookshelf, would I be able to set the temperature to, say, 65 degrees and get the result I want?

Question 3: Given that I want to at least try the experiment of keeping the existing bookshelf (unless responders here talk me out of it), does this have any implications for exactly how far from the ceiling the unit should be installed? (In case it matters, it’s a drop ceiling with lots of room above it.)