Positioning of the tenon board in relation to the template is a little tricky, since there are several variables that affect the fit of the DT tenon within the DT dado. As such, you may want to "sneak up" on the proper fit, so as to avoid cutting the tenon too narrow/loose.
I'd suggest starting by marking the center of the tenon board across the end. Then, mark a pair of lines on either side of the centerline that are 17/64" from the centerline (assuming that you're using the standard 17/32" DT bit). The second pair of lines will be the approximate location of the outside edges of the tenon, 17/32" wide. Position the template so the first pair of cuts will be outside those marks, resulting in a tenon that is wider than needed. Then, move the template slightly toward the face of the jig, and make a second pair of cuts, and check the fit. Repeat as needed, reducing the amount of turn on the template positioning knobs with each pass, until you get the proper fit.
Transferring the outside marks to the side of the board will help in "eyeballing" the position of the bit.
The "proper fit" is difficult to describe, however. You should be able to push the tenon board all the way to the far end of the dado with moderate hand pressure, no mallet-tapping should be required. Remember, the glue will take up a bit more of the space, so the dry fit needs to be in the "Goldilocks" zone - not too tight, not too loose. Doing practice joints on scrap will help you to develop a feel for the amount of pressure needed at the dry-fit stage.
Note, too, that different species of wood will have different friction coefficients. But, practicing on (less expensive) Poplar of about the same width as the actual project should get you close.