HFM Translation rule

I would like to use a custom dimension to translate P&L data at various rates. Currently we use multiple scenarios for this so that we can view actuals and budgets at current, last year and budget rates but it is very time consuming to copy over data each time and the application is now very large.

I have tried using transperiodic as follows:

Hs.TransPeriodic "C4#ConstantRatePY","C4#ReportingRate", "A#RatePY", ""

This works fine at base entity level but the parent values are also being translated at this rate so when you add the translated currency amounts they do not equal the total.