FDA
I too would like to see some maths on this but I do not know enough about it to do that. What seems obvious to me is that if everything else pushes angle of attack towards stall, the only thing the pilot can do is apply forward cyclic to counter it. If the AOA is optimal for the blade speed the rotor will autrotate wherever the cyclic is in respect to the fuselage.
I know this is somewhat controversial but what is important in low Nr autorotation is angle of attack contol.