How do you limit cutting area?

As many are aware, I am using a demo of MadCAM for testing purposes (thanks Joakim!). I am cutting a small bust of Venus De Milo in 3 axis mode (about 3" long and 2.4" square). I want to cut her face and down to about 1.2" from the top, so basically the upper half of the model (Venus is facing up). I tried to adjust the green box defining the stock but that didn't work. I just want to cut the upper half for this test, how do you limit the depth of the tool path generation?

thanks!