How smoothly it probes and and whether it jiggles is a better indicator of correct doneness, and it will vary from brisket to brisket. To address your concern with the flat vs the point, I pull the brisket when the flat is done per the probe and jiggle test (and the point is typically not ready then), let it rest for an hour, then I separate them. I let the flat continue to rest and cube the entire point, season it a little more, mix it with brisket drippings and some bbq sauce, and put them back on the smoker for an hour or two to make burnt ends. Sometimes instead of cubing I will just put the whole point back on the pit and cook until it jiggles the right way.

Protip: The flat is overcooked if it crumbles and falls apart during the pull test with a 1/4" strip. Also, the flat dries out if you slice the entire thing up all at once. Serve it slice by slice in order to preserve moisture.