The ramp code was written by Brian a long time ago, and I admit I have never exactly understood it. The angle is the important value, zero means straight plunge into the work. A value up to 90 is allowed, but it seems to me at 90 it would never get down. Although the ramp dist is an input the code calculates a new ramp distance value based on the tool dia and the ramp angle, so I dont think the value in the DRO really matters.
Sorry I have not got a better answer.