Lighting for stadium grow

I am currently working on designing a medical stadium grow and have some question about lighting. Currently we have are running in a traditional manner, i.e. all plants are grown at the same level. Overhead are 9 1000 watt HPS bulbs in parabolic reflectors. The current thought is to continue running the bulbs vertically without the reflectors. Would it not be more efficient and effective to run them horizontally due to light emitting from the sides and not the ends? The space we are using is roughly 20x20x8.