I’m sorry, but that answer really doesn’t make much sense to me. If there were rules to help determine whether a hunting bow or a stygian short bow is better for a particular situation, then I’d understand. But there really aren’t ANY rules which suggest to apply modifiers for size of a weapon. I mean, sure, we could see that someone using a great sword in a small tunnel would have difficulty swinging it. But it doesn’t actually give you a rule about that.
Also, it seems to me, that if the description of said item would let you know, then each item should have a description so one could make the subjective decision. Interestingly, items do have a stat which could have been useful in determining this, the Encumbrance stat. But weirdly, the two weapons (Hunting and Stygian) have the same value. So it would seem that they should have the same penalty in any given situation.