Excel: Advanced Tiered Pricing

Hello,

I am trying to create a universal formula to help calculate client fees. I am using a sumproduct formula described here to do this. http://mcgimpsey.com/excel/variablerate.html

My problem lies in that some of the clients have a single pricing level, some have a single tier and some have a three tier pricing.

I have all my variables set up in separate columns and each line is a different client. I have a section that calculates the change in rates needed for the formula as describedFee Calculator using Sum Product.xlsx
If anyone can help,it would be hugely appreciated!

Thanks,
Dani