Calculate Percentage Based on Values in Different Rows

[pmmshc1]

Hi

I  hope someone can help me with my query please? I am trying to calculate the percentage for the reason (hours/contract hours).

This is how the data is currently displayed:

The issue is that the contract hours are on a separate line to the hours for the reason. 

I tried the following expression but it only works when a specific record is selected:

=Sum({<[ORIG]=,[ORIG]={AB}>} TOTAL HOURS)
/
Sum({<[ORIG]=,[ORIG]={BALANCE} >} TOTAL CONTRACT_HOURS)

It has worked out the percentage based on the overall total. 

When I filter on the reason, the percentage is not calculated.

I need the expression to calculate the percentage per month, per person, per reason even when all records are displayed. For example, the percentage should be as follows:

Many thanks