I don't think that's right. Let's take some big numbers to make it clearer: you set the jig so the blade is 2" away from the face of the jig. You run a 3" thick piece through it, once from each side. Ignoring the saw kerf, you end up with a 1" tenon. Now you run a 4" thick piece through it, once from each side. Both cuts are 2" from the sides, i.e. right in the middle. No tenon.
-- "To delight in war is a merit in the soldier, a dangerous quality in the captain, and a positive crime in the statesman." George Santayana
"Bring them on." George W. Bush