Non-deductible amounts on "upgrade" contributions

Hi Tessi community!

We are currently building out a mid-level giving program that will include a non-deductible amount for the first time in our organization. One issue we've had while testing the membership organization is that the non-deductible amount when someone "upgrades" to the next level is set to the full amount rather than the difference between the original level and the new level. For example:

The program runs on an annual basis, Level 1 is $1,000 (non-deductible amount is $200), Level 2 is $2,000 (non-deductible amount is $300).

Donation #1: $1,000 for Level 1, processing results in non-deductible amount of $200 on tax receipt.

Donation #2 three months later: additional $1,000 to upgrade to Level 2, processing results in non-deductible amount of $300 on tax receipt. Our desired result would be a non-deductible amount $100.

Does anyone have a remedy for this situation, or is it something we will just have to correct manually? 

Thanks!