For "Rotor Phasing" only vac adv alters the rotor position when running (IE a 11 deg (stamped on arm) can will shift the rotor 11 (dist) degrees around the cap terminal circumference arc. I would drill the (1/2") hole on the cap on top in between the center terminal and the #1 terminal then shine the light on it & you'll see it in action. The can shifts it CCW on a SB and CW on a BB. easiest cure (if needed) is to widen the slot in the top dist metal shaft where the rotor locks into then JBweld the opposite wall to restore the width back to where it was for a snug fit on the rotor so you can shift the rotor around however much is needed.
No. Mechanical advance does have an effect on rotor phasing. Any advance be it mechanical or vacuum changes rotor phasing. I think you are mixing rotor to reluctor phasing. The post is about cap to rotor phasing. You want the cap to be phased perfectly at peak tq rpm with 100% load. To test you must simulate low manifold vacuum(if you have a vacuum advance or load sensing ignition.) The less load, the less important rotor phasing becomes.
