Based on your depth you have have the Mitras fairly high so the spread "should" counteract the issue with the brace providing the brace is clear glass.
Having said that as you are 36" wide two units either side would of course be optimum, however start with 3 see how you get on.
Thank you for the quick feeback. The tank is built of 3/4" acrylic. I think i will go with 3 for now as i like the look of some shadows in the tank. It makes it look like some ocean depth. But whats great about the Mitras is the expandability with out changing out whole fixtures/set ups.