Assuming you are only cutting in 2 axes, the Z begin, Z end, and Z center are all the same. The thing I always did was just hit "0" and "inc set", obviously meaning it is 0.0000 incrementally from the Z begin
Another thing too, with the old prototraks, you do not approach to and release from tool compensation. You set it on from the get-go in any chain of events. You can not change from center to left or right, or any switch between the 3 while running any chain of events. But, you would still want to approach and release from your part.
To simplify inputting in a chain of events, once the first even is in place, you could simply put "0" and "inc set" (for that matter just hit "inc set") for the X begin, Y begin, Z rapid, and Z begin of each following event. This obviously tells the control that each even is starting from the end point of the previous event.
But, if you say you are cutting a corner radius on on rectangle, just use the "con rad" (connecting radius) in the mill event. It will put a radius between that mill even and the next event