Hyperion Financial Reporting - Calculating Percent of Subtotals?

I am intending to use the Percent Of Total formula to calculate the percentage of a subtotal.  However, the formula provides a percent of all.  Is there a way to accomplish this?

I have included at the bottom an image of the actual grid, but for simplicity provided a basic example of the results I expect to come back and the results I'm actually getting back.

Anticipated Results:

			A	B
Cost Center System Defined Member List Lev0	Basis Type Children of Tier_2	Recipient Descendants of All_Recipients	% PercentofTotal([B],[B,3])	Total
CC_A	BT_1	RP_a	15%	15
CC_A	BT_1	RP_b