I agree with Thoraeon. If I'm solo I just forgo white proc and go as Dnc/Thf for TH, but if I'm in a group with a Thf I'll go Dnc/xxx to try for white.
I also agree with Ariaum on no difference in white proc rate between EP and stronger mobs. Just the more mobs you can kill the more likely you are to trigger white.
I had a dry spell recently and went a good 15 runs or so with no white, but in my last 5 runs I've gone 1,1,0,2,0. It just depends if SE is watching or not ;)