This one I used normal mapping and it didn't give an option for "up / down" like bump mapping did, only Tangent Space/World/Object.
However, it probably is inverted because of how Vray handles bump and normal maps. With Bump maps a negative value is needed (-0.67 is usually best for scales on reptiles. -1.00+ for rocks and stuff), so I just went with that assuming normal maps needed a negative value too. I guess I was wrong (I usually just use bump maps X3 )
Ah, I see. Yeah, since normal maps operate on the X and Y as well as the Z, up/down wouldn't describe the effect fully. I suppose the up/down toggle on bump maps flips whether black is maximum depression, or maximum bump. That should have the same effect as using a negative value or positive value though. I dunno the internals of v-ray though since I've never used it.
I haven't really used normal mapping myself either. Probably will start to when I finally reach the level where I can accurately model a higher resolution model to generate the normal map from.