The rail thickness and shape changes from nose to tail, and not all rails are the same shape. You could have one for the nose, middle and tail sections. I think the tails are usually pretty square, so they are pretty simple.
My boards have a flat deck, some are slightly concave, so I have fuller rails. I used the tool to get a nice round shape mainly in the middle of the board. But for most of the modern boards I’m seeing here, the basic shape seems to be very close, and it’s easier to do than making rail bands with a flat edge.
My old shaper told me to draw a lot of lines when you do the rails. 1/2" intervals on the top, side and bottom. Then follow those lines to keep things straight when you cut the rails.