I passed the question onto the PCC and they are investigating.
The PCC weren't much help either:
The costing for NPAS is a formula set by the Home Office which has been in place for a number of years. It is difficult to compare Hampshire and Isle of Wight with a force such as GMP due to the extreme difference in size of force, demographic, social and economic characteristics. For example Hampshire and the Isle of Wight has a much more rural area than GMP.
Still as clear as mud.