why the huge gap on raid rewards tiers

For the Speeder Bike raid (I noticed similar before on Krayt also)

between 36mil and 108mil almost a 3 fold step
and again 208mil to 424mil over a double up

and yet other reward tiers have reasonably close increments (16 to 23.2 to 36, 108 to 125.6 to 144)

Anyone know why, very odd numbering system