rectangular sizing

I’m wondering if there’s an advantage to doing a rectangular, rather than square, build size… For instance, I’m considering perhaps a 6 ft by 3 ft build… It seems like having one dimension shorter than the other would prevent issues with flexing, but I don’t know if I’m missing something on this. If this is a correct assumption, would it be better to have the shorter dimension conduit on the top or the bottom portion of the gantry?