Quick follow up, just after poking around with SiF + Foliax for a few minutes:
The one thing that jumps out at me looking at the tech tree is that there's a fair amount of overlap with Foliax and Space Age tech. For example, Foliax and Space Age both have a foundry but have different requirements for the same machine. It might make sense to match and compress similar tech in the tree if it's not a huge logistical hurdle, just for the sake of continuity and eliminating redundant research paths.
I can see how it might be a problem, if other mods have different requirements and SiF is supposed to accommodate technologies from other planets. For the base game + DLC tech, though, it seems logical.
I don't know, so just throwing it out there as a consideration.