Qweesdy i'm unable to tell from your wording whether you were placing stabilizers at x% efficiency or if you were adjusting reactor size until your
stabilization was at x%.
There is a huge difference.
Reactor blocks give a certain amount of potential energy. You reach that potential at 100% stabilization. Maybe there are other side effects to low stabilization other than reduced power output? I dunno yet, and i'm not sure it's been tested out fully by the community because of how new it is. If you continue adding reactor blocks (or removing stabilizer blocks) and can see your stabilization reducing, you will also see your power regen reducing.
In other words, if your reactor is exactly 100% stable and you add more reactor blocks, you will actually get less power out of your reactor. Not sure if this is what you're experiencing, but it sounds like it may be, as you seemed to be getting less and less as you added to the reactor.
I also haven't heard anything about multiple reactors giving extra chamber options. Is it any different with two reactors than it would be if you just laid separate conduit lines to more chambers?
Not so. Here's an octahedral station i made in creative, just messing around on the dev builds over the last few months. Reactor in the middle and stabilizers in chunks as far away from the reactor as i could manage. I believe it's 200k power and about 100m in each direction out from the center (200m across on the long dimensions).
Is it strange that i have six chunks of stabilizers, each about the size of my reactor? Sure is, but it takes more stabilizers if you're not going to put them all at 100% efficiency 15km away