SSAS Cube in Excel - Show only applicable rows with KPI?
Thanks to @ConcernedOfTunbridgeWells for pointing me in the right direction on this.

The issue was with the status expression.

Since it ALWAYS returns a 1, 0 or -1 it didn't account for NULLs.

I added a check at the beginning of the expression:

CASE WHEN IsEmpty(KpiValue("MyKPI")) THEN NULL

...which correctly leaves  those fields empty.