If you are interested in orienting your bulbs to maximize PAR take a looksie:
Advanced Aquarist Feature Article
I believe your reflector would fall under the spiderlight category.
Looking at that plot, I don't think it would make a huge difference which way you orient the bulbs if you are lighting a 24x24 sq. area with it. At 12 inches deep there is more par spread out along the 6" mark of both sides of the X axis of the bulb. So depending on where you are placing corals you might want to take the into consideration.