I believe the across and down, are the image coordinates. So the image it uses is a sprite that is made up of 64 smaller images that create an animation.
I can imagine that if you find the model (plane) that the decal uses and change that for a bigger plane, the image would stretch to fit, thus, giving the impression of a bigger decal.
This is only guess work as I haven't actually tried it myself yet.
Cheers
Jay.
