@OrganicMarble I see, well I don't know anywhere near enough about chemistry to even think of nitpicking this. Might as well make an edit to the OP. I have similar doubts from often seeing liquid solutions described as separate ions and wonder if these are actually two different chemicals in a homogenous mixture, or somehow they can be considered one since the ions should attract and stick to each other.

I forgot the note that all substances are gasses at the right combination of temperature and pressure. Will edit the OP. I realize gasses are far less dense, but iirc there are still some tiny sats that use cold gas because liquid tanks need a gas pressurization tank anyway and all of that would be too heavy for it. But mostly my q is of curiosity. Why would gaseous monoprop chemicals apparently not exist?

And you know, via the topdown diagram, i can see now the limiting geometry is the radius between center and outer walls. Those tanks barely fit behind the outer wall. This brings up one more thing tho: The center section has 2 helium tanks, but how much of the engine sticks up into it? Cant find good diagram/pics of that. If needed i can do another question about this and structural loads, thanks for the info so far.

but leaving them out to make a bigger section was apparently not an option. This is probably the key then. I did not think about Saturn 5 launch loads on the CSM at all, (but correct me if I'm wrong, the escape system only pulls the CM, not SM/LM). This also reminded me that the CSM was originally designed for direct ascent, engine was 2x more powerful than necessary. I guess that doesn't matter in the face of Saturn 5 launch loads anyway.