Exception aggregation on a key figure - only for reports?

Hello. experts!

Desperately need your advice.

In Cube 2 I have Cumulative Key Figure (Price)defined as SUM adn Exception aggregation is AVG based on 0mat_sales.

Data is moved from Cube1 to Cube2. Data in Cube 1 is more detailed(invoice level), data in Cube 2 is aggregated on Customer, time and material level.

When Price is calulated, its adding up as many times as there invoices for specific time, material and customer. I thought that Exception aggregation would take care of the AVG but it does not look it. Does Exception aggregation only works when data is looked thriugh BEX, not when mobing from one Cube to another?