[Delphinus]

Why would you get a better spread if you mount your halides front to back as opposed to parallel with your tank?

I would think that it depends on the reflector. Just using a reflector one way or the other shouldn't make a difference .... it depends on the spread that a reflector gives you. I thought that the ones for perpendicular had a wider spread or something like that. The shape mustn't be a perfectly symmetrical 2'x2' area.

BUT ... I don't have those kind myself so I can't really offer any practical advice based on experience ... sorry. I myself went with the 4' reflector running the length of the tank. I'm sure it's not "optimal" but then again I'm pretty happy with the results so far. So ... whatever you do, go with whatever makes most sense for you. Try it out both ways and see if you notice a difference.