It seems to me that headwind component cannot be dismissed from a discussion about power-off range speeds.
For example; If for a given acft the power-off range speed is 69kts and it is autorotating at 69kts into a 69kt headwind then groundspeed would be zero so distance covered would also be zero.
Therefore an IAS greater than 69kts must give a greater distance covered, ie more than zero.
If you take this concept a step further and say the headwind is now reduced to 68kts then the groundspeed is 1kt, would you achieve a greater range if you increase IAS to 70 kts thereby giving you a groundspeed of 2kts? Or 71 kts giving a groundspeed of 3kts? etc, etc.