Charges and billing rule caps

We generally run billing rules from rate cards with caps, per the contracts we have with our clients. While we want to make sure we don't invoice more than what is allowed (hence the cap) we are finding that OpenAir won't look at time that is leftover after caps are being hit. To help break this down, I will use very simple numbers for an example.

Rate card = $50 per hour

Billing cap is $100

Resource logs 8 hours to project/task

If we have adjust time entries to fit under cap, then charges will be created for $100 for 2 hours of resource time. If we get additional funds to increase the cap, how do I pick up the leftover 6 hours? OA doesn't want to look at the leftover hours/time entry since it thinks it is already taken care. If I choose 'don't adjust time to fit under cap', then it doesn't pick up the original $100 charge at all in the first place.