I'm going to go against the grain here some, but what my advice really is, is try it and see what works best for you.

I use the black 20x28 concrete tubs (not sure which it is on their size scale) and generally keep 1.3 rats per tub, occasionally I'll do 1.4 in them and do not have any trouble. Normally if I'm doing a 1.4 cage, it's because of a litter of rainbow boa's being born or clutch of woma's hatching and I know I'm going to be feeding out a lot of extra rat pinkys and just wanting to boost pinky production. I don't pull moms or rotate males through cages, I set up a colony and leave it and it works great for me. One thing that might be helping this work better for me, is I pull a lot of nursing rat stuff to feed, from pinky's all the way up to weaning stuff and I try to pull a bit from each cage instead of everything from just one, so I take a little of the baby nursing work off each cage constantly. Only a few rats from any given litter ever normally actually get weaned.

Try it and see what works for you, if you plan to raise litters all the way up to being weaned, you may need to cut back on the number of adults per cage.