Definitely get it in writing! The 'old' agreement was that you could add:
Helicopters with skids: Nothing
Helicopters with wheels: 5 min per sortie
Fast Jets: 10 min per sortie
Multis: 15 min per sortie
A straight 'percentage' of 5% seems rather low. Alternatively - and I've said this countless times - open a civil logbook and log all your flights from chocks away to chocks under in that logbook. Carry forward all previous time with the appropriate 'allowance' approved by the CAA already included.