Cube View - Average column based on fixed denominator of 4; numerator is column that have data

I can see two options, but the main strategy is really the same: don't reason in terms of columns, but in terms of intersections. You can easily have code that checks those 4 intersections, and calculates what you need.

The practicalities boil down to a choice between a Dynamic Calc formula, placed on something like a UD8 member; and a custom GetDataCell function. The main difference is that the former can be surfaced in various ways, it's a bit more like simple cube data; whereas the latter is strictly limited to Cube Views.