The location of the rim dowel stick hole is interdependent with the location of the neck dowel stick hole. A lot of things come into consideration here, like the height of the tone ring, and the depth of the rim. Also, the neck should cover the place where the outermost lamination of the rim meets itself, so try to center the hole on that joint. I like for the end of the scoop of the neck  to come just even with the top of the head. On the neck, measure the space from the front of the dowel stick hole to the face of the scoop, this measurement tells us how far back from the top of the tone ring the rim dowel stick hole will begin. Make note of your measurement. Put the tone ring on or subtract its height from your measurement. Find the joint where the outermost lamination of the rim meets itself, measure parallel with the joint beginning from the front face of the rim and make a mark according to your measurements. Check it twice. Base the rest of the hole measurements on that, mark it clearly. I typically drill a small hole and then cut it out the rest of the way with a coping saw. Then a file can be used to clean up the edges. The fit of the dowel stick should be snug but not tight, a little loose may be okay but I like snug.