wrote
Do you have research that shows direct sun on a window unit has
no effect? If direct sun on a window can add heat to a room, one
would think that same heat applied to both the window and a
window unit AC would have an effect.

I've seen some studies done with CENTRAL AC, where shading
the CONDENSER made no material difference because as you
say, it's the air temp that counts. But I have not seen the same
for window units and for obvious reasons I don't believe the results
for split systems can be applied to self-contained window units.

Why would it not apply? A window unit is sort of a mini-mini split.
Everything is in one big box instead of split apart by a piece of copper
tubing. The condenser coil is covered with sheet metal and has a fan
blowing on I it, just like a big unit. The fan sucks in air from the side
vent, blows it across the coil.

What may be different is the slinger ring on the fan. That can affect the
operating temperature. If the air is very dry, there will be little
condensate for the fan to sling onto the coil. Does that make a difference
in the readings the OP is getting? I don't really know. Easy enough to
test though, by spraying some water into the vents while it is operating.
It may reduce the pressures in the system and lessen the motor load of the
compressor.