Option A is better then option B. The main limitation in dispersion when placing the speaker sideways like that is the driver to driver distance. A larger distance between the drivers leads to a narrower dispersion before a cancellation at the crossover frequencies when the sound waves from the two driver are out of sync/phase as you move off to one side or the other. The dispersion at the high frequencies will still be more limited with the waveguide vertical (+-40 degrees instead of +-90) but that's less of an issue then having a hole in the response in the midrange, the rolloff at the top end is gradual. You will still get a hole in the response off axis with option A but you get more coverage before that happens (around +- 15 degrees) with the tighter spacing.