There are too many factors to generalize ideal levels, IMHO. Yes photoinhibition occurs when you expose corals to too much light, as it effects their metabolism and ability to thrive in the system.
Light, nutrients, and flow all play a huge role in determining how happy your corals are. I've had zoas in my nanocube (skimmer, dosing, GFO, MH lights) under a PAR of 200 look unhappy because they were getting too much light, and I moved them down to a PAR of about 100. In my new tank (LED, no skimming, no GFO)...those same zoas stretched at the bottom of the tank and are now directly under the LEDs getting hammered with light and look to be in better condition than they were in the cube.
I think PAR is helpful in giving your tank a workable "gradient" for coral placement...but trying to pinpoint an ideal number to place a given coral seems to be fruitless from what I've seen. As long as you're within an acceptable range, you should be fine.
FWIW, I have zoas in my 20 that are almost completely shaded and thriving that close up completely and melt when exposed to direct light...