the problem is the discount amount you are entering
you nee to enter the total discount, not an incremental discount.
for example, you want 12 - 99 to be 1.49 ea. the original price is 2.49, so
2.49 - 1.49 = 1.00
the discount amount for 12 - 99 should be 1.00, however you entered 0.59.
each break amount needs to the entire discount amount from the original price.
The abs function is choosing which one to apply, only one of them gets applied at any one time.