Some Decals are Offset

[Empyre]

When I had a projectile leave a DoomImpScorch decal, the decal appears right where the projectile hit, but when the projectile is set to leave a CacoScorch, the decal is always either above or below where the projectile hits. Why is that?

I have even seen a decal that appears in 4 places: above-right, above-left, below-right, and below-left.

 

I am making this for Zandronum, btw, and yes, I asked in their forums, too.