I get it... I will read it over again later to "get it" some more!

Chuck

That is the best way I do it. My cutters cut 7/16 so my rails and
stiles are 2 7/16. You will loose the 7/16 with the cope cut so your
left with 2" on each side. Take the total door width and subtract 4"
and that's the mesurment from inside the tongue to inside the tongue.
It does not matter if your door is some odd ball size your rails will
be 4" narrower than the width of the door. Then take off another 1/16
to 1/8 for raised panels or just a 1/16 for plywood flat panels.