Formula in Contributor report

[bladeless]

I have eList with structure like that:
-1
|-2
|-3
In Contributor report, which use this eList to create report, there are field B,C and field which is result of calculation: A=B/C.
If report created for element 2 result is A2, for element 3 result is A3, for element 1 result is A1 = A2+A3 but this result is wrong because it is not equal to B1/C1(B1=B2+B3, C1=C2+C3). All formula I create in Planning Analyst. Could you say how to resolve this problem?