I defy anyone to visually differentiate between 89 and 91 degrees nose down.
Bill Finagin, who has done thousands of spins in Pitts and other types, teaches that you need to put the controls to neutral and take ALL power off, which means that you don't need to worry about stick forward or stick back. Look along the nose - then, "nose goes to too much rudder". It's a bit disconcerting when you experience it for the first time, but applying corrective rudder on this basis applies equally well to upright or inverted spins. Once the spin stops, recover.