SSAS 2012 - Calculated Member that uses measures at different grains

I'm trying to set up a calculated member - budget remaining that is dependent on two native measures - expenses and budget - that come from two different measure groups, and the former of which has a finer grain size.

When I drill down to the finest grain in the hierarchy, which is one level below the budget grain, the budget remaining measure has blank values as expected, but the calculated member shows up as if the budget field were a zero instead of a null. For example if my expenses values is 200, my budget shows as a blank cell, but my budget remaining show up as (-200) when it should also be blank.

Is there any way I can get my calculated members to not show values at inappropriate levels of my hierarchy?

I have the IgnoreUnrelatedDimensions property set to 'False' on all my measure groups and tried changing the Non_Empty_Behaviour property values, but to no avail.

Any suggestions or insight would me much appreciated!

Thanks