Cap on parish Portions and payment timetables - Public forum - Planning Advisory Service (PAS)

We are having a lot of back and forth with a parish councillor about the cap and portions. My question is has anyone else set up a payment timetable agreed directly with a parish instead of the payment periods in 59 D (3) and (4)?

If you did was this just decided or did you seek legal advise?

If you have when you calculate the portion did you calculate the percentage on the lump sum when it was received or on each portions in accordance with the agreed time table in order to avoid the cap issue?

Any help would be much appreciated.