u want to ramp a cutter from z0 to z-.375 over 18 inches? is this correct? Do u draw in Alphacam, or another software and inport a DXF?
If you click on the 3d button you will get xyz coordinates with the increments on the graph, set the view to what u want to draw in relation to how the panel will be positioned on the machine. Draw the part as you change views and planes, when you get to your line start it on the plane at 0 where you want it then change the view so u can pick the z- position to finish the line.
This is a quick basic explanation but if u have experience it wont take u too long, if u screw around with it a bit.