Tax Class and Earning code

[Ktonthat]

( A ) I have a YTD Taxable Gross amount from CAN_TAX_BALANCE table
It has TAX_CLASS_CAN = 'TRV'( True RL )

( B ) I have also several earning codes from CAN_ERN_BALANCE in the same period

How do i know which earning codes contribute to the YTD Taxable Gross ?
I thought of the checkbox "subject true RL" ( below ) but it did not balance between the earning codes and the YTD Taxable Gross