there   really is no reason at all to play pp once you have 20 mil def and 20 mil off,  unless you want points. or have 150k in lights and heavies to burn off.  the only point is for a conversion of weak troops to large troops.     also  if you have precise attacks  you can stretch your troops out as far as possible.      a calculator is the only way to do this,  if you are not using a calculator you are wasting your troop units.   so  think about what the point is   of PP   and know the  rewards  are capped.
my noramal payouts  are 20 mil in def    the highest I usually see is 34 mil.    for off   the usual payouts are 15-20 mil    the highest I get  are 54mil.
if anyone has better  payouts  I would like to see them!!!   seriously.
the bank is one total bank.     so don't expect large payouts on low levels   levels are 1-170.    so the  higher  you  play the bigger the reward.    stay in the same  range of positions  and this will happen.  if you lose your army with no rewards  wait until you can knock down one more position in that range  don't  play  lower ones  until you get your payout.
also if you don't have 100k or more in lights and heavies     or at least 20 mil in phalanx and cav, you will not get big payout.    but that is the  reason there is no reason to play them,   what you put into them you get back out of them.  it is an upgrade in units  not a bigger army.     which  makes this aspect silly.
and think about this   if you are only  gonna get  a certain amount of power   once you get it    no reason to play again   as it will cost you 24 mil + for next payout.