The ricasso is normally a good spot, but with the handle installed the diamond point will not be able to get to the spot. On a completed knife, it would need a flat spot on the blade above the bevel. A full flat grind doesn't have any flat spots to test. If the handle has not been installed, most any place and be tested. The test WILL leave a dimple in the blade at each test spot.
In a post you mentioned a desire to send a knife to someone to do a Rc testing on. If you wish to ship to Alabama I'll be happy to test it. I've got the Grizzly HR150 Clone Rc tester and would be happy to rest it for you. It will require the blade to have a flat spot that the point can get to.