Does this help?
As the advancing blade passes over the tailboom, it gets faster and produces more lift, which means that it climbs.
Because of the V2 part of the lift formula, the lift produced is way more than that of the retreating blade, and its maximum relative airspeed (and therefore lift) is gained at the front of the disc, because the climb starts 90° after it starts to increase its relative speed, and its maximum lift point is 90° after that, which is a shift of 180° overall. Thus there is a 90° difference between maximum flapping velocity (abeam) and displacement (at the front).
As well, there is more induced flow at the rear of the disc which increases the difference between the front and rear angles of attack (less at the rear)
.
Note: This is why the nose lifts when you apply collective pitch, or drops when you reduce it, so if the engine fails and you don’t apply rear cyclic to correct this tendency, you could get into an unrecoverable situation. The moral: don’t take your hand off the cyclic!
I know Shawn Coyle has his Little Red Book of Autorotations out now - perhaps he can help.
Phil