Executing a fox im getting a strange result.
Just with the planning area filtered Im trying to copy the KF % to the KF Amount:
0AMOUNT = ZOV_PERC.
The system reads the records but dont fill the KF Amount.
Replacing Amount by Quantity the system modified the records. The problem is that the InfoCube assign the planning area I dont have KF Quantity. 
Another test I did was replacing the planning area. Changing the planning area filtered in the level, the system executes the function 0AMOUNT = ZOV_PERC.