Sorry that I can't answer specifically for the VTX, but the NC brackets can be installed within about a 4" range. I didn't like that the shield sat about 3" above the headlight bucket with the recommended install position, so lowered it.
agree, would want the shield pretty close to the headlight within an inch or so for sure, if possible.
I will call national cycle tomorrow since sounds like no one put a vtx1800 NC switchblade 2-up on a valkyrie to see what they say. I found the shield somewhat local asking 80 bucks.