The fuel ring is what you look for to tune for WOT.
It should be .080-.100 wide (some guys can ring it under .080 but you have to be on top of the tune up to run it that close to the edge...a simple weather change can run you right into detonation) and you need to use a magnifyer of some sort and look down into the shell where the porcelain meets the shell. That's where you should see the fuel ring.
I think I have some ok pictures. I'll see if I can find them and post them.