Most people move male to female, because the female will presumably want her own tub once she ovulates. And it's her comfort zone, so maybe she'll be less stressed and happier to mate.

I'm tending to do the reverse right now because I still only have rack space for about half my collection. And my females share the big tanks happily, while my males will start wrestling with each other staring around January or February. So the boys get their own tubs during breeding season.