In my experience, the larger the polyp/mouth, the less light it usually likes. If it inflates to a large size, it probably likes lower light. The smaller polyped, harder pieces like Favia, Favites, Cyphastrea, Platygyra, Turbinaria, Mycedium, and Hydnophoras can be placed higher in the aquarium with more flow.
Pieces like Scolymia, Cynarina, Trachyphyllia, Fungia, and other large single mouth corals should be placed on the bottom.
Corals that fall somewhere in between are Lobophyllia, Symphyllia, Euphyllia, Caulastrea, Echinophyllia, Acanthastrea, Micromussa, Cataphyllia.
I don't know where to place Blastomussa in that scale. I have a Merletti getting direct 400w 10K MH lighting and some Wellsi's getting medium to weak 175w MH lighting.
Most corals can be kept under a large range of lighting. The most important thing not to do is subject them to too much light. Way more damage can be done in one day under too much light vs weeks or months under too little light, IMO.
I would be careful with your 400's. Even on the bottom of my 24'' tank, my Scolymias slowly bleached from my lighting. Once they were placed under 175's, they made a full recovery. Sometimes it can be difficult to keep high light SPS in the same tank as low light LPS. You have to be a little creative, and make shaded areas or Caves.