The plan bonus should end once it equals the total growth bonus. Here is the
formula that I use to calculate the Plan bonus:

=IF(H160,0,IF(SUM(F$16:$F17)=$C$12,(SUM($G$16:$G $27)),0))

where H16=Plan bonus, sum(f16:f17)=increase over best, C12= monthly plan,
sum(g16:g27) =growth bonus

My data is below:
Monthly Plan $33,829
Monthly 2mo avg increase growth Plan
Sales over best bonus bonus
$7,089 $7,089 $7,089 $- $-
$16,385 $11,737 $4,648 $106.90 $-
$42,591 $29,488 $17,751 $408.27 $-
$25,636 $33,829 $4,341 $99.85 $615.03
$56,416 $33,829 $- $- $-
$5,630 $31,023 $- $- $615.03