Calculation of sums of columns

Attached, you will find an Excel sheet created from a Flexmonster export that illustrates my question.
In the Excel sheet, you will find three columns: “Menge”, “Durchschnitt von Wert EK DSchnitt”, and “Menge x EK”, where “Menge” is the amount of an item, “Durchschnitt von Wert EK DSchnitt” is the average of this items purchase prices over a timeframe and “Menge x EK” is a simple multiplication of the previous two values.
In row 9, you can see sums and, in the case of the average purchasing prices, an average generated by Flexmonster for these three values. The sum of the “Menge x EK” column is also calculated by the underlying formula of multiplying the other two values, which leads to an incorrect sum as it is based on the average of an average price. (The correct value can be seen at the bottom of the column.
So my question is this: Is it possible to change the way column/row sums are calculated to actually sum up the required values instead of applying the defined formula for a cell to its sum? Or is this something that we have to change on our side?