From: United States
Like I said, far too many exceptions to this ideal RB height. You say Payton, I say Brown. You say Sanders, I say Dickerson. You say Tomlinson, I say Allen. You say Faulk, I say Harris. You say Thomas, I say Simpson, etc...
I don't think height, or lack of it, matters that much. Far more important is foot speed, explosion, low center of gravity and strength. Sure, generally speaking, smaller guys tend to have better foot speed, but that's not automatic either.
As far as being less visible to the defenders, why not have 5'-2" RB's dominating the league?
Arm length aids in blocking, receiving and ball security.