The depth is completely controlled by the size of the holes. Using a wider-angle bit as Phil suggests will make shallower holes.
I could add a visual to the display to tell you the deepest possible cut it will make, based on your maximum hole size. The math is easy, and already done elsewhere in the code.
MaxDepth = (MaxDiameter/2) / Tangent(BitAngle/2)
So, for a 60 degree bit, and 1/8" diameter holes:
MaxDepth = (0.125 / 2) / Tan(60/2)
MaxDepth = 0.108"
For a 60 degree bit and 1/4" holes:
MaxDepth = (0.25 / 2) / Tan(60/2)
MaxDepth = 0.216"