When I first started "Convexing" I used a Spyderco sharp maker to put a 20 degree primary bevel and a 15 degree secondary bevel and then using a mouse board and grit paper convexed the secondary into the primary for an appleseed shape....after doing it for a few knives I can now get very close to this on the belt sander...so I never really measure any more...but I doubt I go lower than a 20 degree angle on the primary bevel aspect of a convex blade.

Spyderco said they had checked all different angles and found 20 degrees either side to be the most resilient.