Surely it's not rocket science to conclude that at low rpm your cyclic control is very ineffective and so you have no way of controlling the disc flapping if you choose to raise the lever to slow down the rotors - therefore as Bell says, mast bumping may occur which I think is universally accepted as a bad thing.
Interested as to a detailed explanation of why the 11 o'clock is the lowest point for the rotors........maybe it is a local time v GMT answer
