Well, you have to figure out the spread of your PAR38 lamp and what type of corals you intend to keep. I have never purchased one for corals, but I use an all white one over my refugium that I got from home depot and it's got a pretty tight spread. I have it 16 inches above the water and I'm getting about a good 12" of light. The surrounding light isn't coral worthy IMO
, so you'll have to place this lamp pretty high in order to get decent coverage.
That fixture you have in your post is overkill for your tank, but you can turn it down to fit your needs. HTH