What exactly determines the size of your weapons/ mount?

[Crimson_Hunter]

Your race. That defines it. Not all, some mounts are the same for all races.

Oh yeah I do remember some things like Goobue and some spoilery mounts don't change size.
Would you happen to know what category each race falls under?

Which is kind of weird. My fc mate is bigger than me, yet some of my mounts are bigger than his. O_o

What are your and your FC mate's races?