Hellion: If you got 11-13m coins from the 1.25b hp boss, it means you deal 137.5m - 162.5m damage.
With the 6.25b hp boss, your total percentage dealt is 2.2% - 2.6%.
You should be getting only 2.2m - 2.6m coins with the old damage you deal.
Assuming the time has been doubled, therefore you deal 2x the damage, your new haul should now be 4.4m - 5.2m coins.
That just makes no sense too me or maybe i am just too tired for my brain to work properly atm.