Why am I getting null values in my view?

My data looks like this (blended):

I want to calculate the Acceptance% (acceptedreplacementcount/requestedcount), by department, item name, and replacementsource. I created one of these calculations each for Shopper and Machine:

IF  ATTR([Substitutions_Shopper_Behavior].[Replacementsource]) = 'Shopper'

THEN zn([AcceptedReplacementcount/Requestedcount])

ELSE NULL END

When I create the view with departments and item names in rows, I get no results for cucumbers since there is more than one replacement source. I only get results if all records for a given department/item are from the same source. How do I fix this?