About 2 degrees per side on the tracking pulley. On the one I built like this Kolomazzo https://mechanicguides.com/best-belt-grinders/
, I cut the face of the contact wheel square, and crowned the top idler. I left about a 1/4" flat in the center.
Here is a pic I have handy right now, I can take a better one tomorrow. You can't see the crown in the picture at all.