PAR -> photosynthetically available radiation
The amount of light reaching the coral that it can use in the process of photosynthesis.
There probably are some SPS
corals that really do need a certain level of intensity to really grow and thrive but i doubt there are very many that would need a whole lot more then you would be able to provide with the light you have in such a shallow tank. Something you will just have to do a bit of trial an error on. Start with some of the easier ones and move your way up.