Average Summary Not Working
 

My pivot table set up like this:
Column A is staff name
Col B is hours worked
Col C is hours billed
Col D is productivity

The productivity for each staff comes out accurate but the summary does not.
The result I am looking for is total hours worked, total hours billed and
productivity (billed/worked hrs). I tried custom calculation and also tried
having 2 subtotals (one for sum and one for average) but still can't get the
productivity for all staff correct. Advice?