It depends on what you are looking for in dispersion. Remember that a center fill often sits between two other columns and you only desire a certain range of coverage to avoid phasing issues. Depending on your situation, a 328 on its side might be perfect. These speakers are used regularly as stage monitors, and are actually designed to be used in either orientation. The sound is not different, only the projection angles.

I also have my 328s set up so I can fly them from a light truss horizontally or vertically (make sure you know what you are doing before attempting this), and will purchase one more 328 so I can use 3 side to side to accomplish a roughly 180 degree coverage in horizontal orientation. This is a sort of flying use of a middle 328Ai, and I expect it to cover intelligibility issues in the center area of the audience when the outer units are widely spaced, while providing better coverage to upper and stage front seating... areas the 60 degree vertical coverage in standard orientation can struggle covering.

All that isn't an answer to your request, but might shine a light on an optional thought or two...