JVL,
I went through this same exercise a while back and published what I did with my 7W diode laser here:
I was able to use the layers available to do a “first pass”, then fine tune a second pass between the three best Z-heights to really find the best Z-Height for my laser. You could use this same technique. It’s a little tedious, but the layer dialog box in LB makes it better than having to click on each layer to change.