"eco progression in faf is something that is not intuitive, noobs frequently ring t1 MeX with storages or forget to ring t3 mex because it’s not clear that this is unholy inefficient"
Well this is somewhat true I suppose, but I wouldn't say that it means there is a "balance problem" to fix. Noobs just need to pay some attention and learn the most efficient path is:
build T1 mex--->upgrade safe T1 mexes--->cap T2 mexes--->upgrade capped T2 mexes.
So I don't think we really need to do much about mex storage adjacency. If anything, we could easily increase t1 storage adjacency so that a fully capped t1 mex gives 4 mass total. It would still be significantly less efficient than upgrading the mex to t2, so it doesn't really matter, but would be just a bit less punishing for noobs.
I don't think storage adjacency is OP, but I have had a small lingering feeling that storages could be a tiny bit more beneficial for t2 mexes, and slightly less beneficial for t3 mexes. It would make eco upgrade choices a little less of a big decision, since in many games a t3 mex is a very expensive investment with a large payoff if you make it work. Maybe something like 10 mass for a capped t2 mex, and 25 mass for a capped t3 (compared to 9 vs 27) would smooth the economy upgrade path sufficiently. (maybe some cost adjustments would be justified as well) But I must emphasize I'm quite uncertain if smoothing economy upgrades would be an improvement, or how to best approach it. Maybe it makes the game a lot more strategic and interesting to have t3 mexes a very expensive and very effective upgrade, and a more linear or smoothed out upgrade path would be more boring.