I am not trying to be intentionally vague here, but I also don't want to dump out tons of IC information for people to profit from. Armor layering is a very important thing, and right now, layering rules seem to be setup in such a way that while it might make some sense from a tier or price standpoint what can and cannot be mixed and matched, often times these interactions simply don't make any sense.
I'm not sure if this is accidental, but I would assume that it is at this point, as I don't recall seeing any activity on this subject in the past few years.
Example: Protek pants are described as being kevlar weave with maybe some ballistic plate inserted. They're heavy, but they're not described as being particularly bulky or awkward to move or wear. And yet, we can't wear non-protek trench coats over them. Why? If I'd like to use lower tier, less effective garments in conjunction with some nice things, I don't see that as particularly game-breaking, personally. But then again, I could be entirely wrong on this subject.
Could we get some common sense inserted? Example below:
Low Layer: Bodysuits
Mid Layer: Pants, Shirts, Plated armor pieces.
Outer Layer: Trenches, Helmets, Gloves
The Du-wear bodysuit is described as being a skin-tight leather suit. I'd imagine I'd be able to wear pants or a shirt over it, not under it. With other, nicer bodysuits it makes sense why you are not intended to wear layers over it, but I'm just using this as one example here.