What I do is for op 1, specify the amount into the material z0 will be, although I don't take a lot off in the first op, but this doesn't matter much. For the second op, specify z=0 at the finished thickness. If you're not sure of the starting thickness of the stock, you can set the starting surface higher to enable an extra pass in case it's thicker. You can add block deletes to bypass this first pass if necessary. Be careful if you do so though, that you bypass information that might be needed if the block delete function is on.
Newtexas2006 is right, you and the setup man/operator need to be on the same page. I'm lucky; my Haas operator is very sharp and knows what I mean most of the time, but I still give him really good setup instructions; more info is better than not enough
HTH
Mark
Insanity "doing the same thing and expecting a different result"
Mark
www.mcoates.com