Using cumulative aggregration and group by in a line chart

[e487]

Hello all,

I'm working with a calculated item which aggregates a percentage value cumulatively. The column it's based on has the data as a percentage of the total within that category. So this calculation should give a percentage running from 100% to 0 within each separate category.

I've managed to get the data to display correctly in a crosstab:

However when I'm trying to get the data displayed in a line graph the aggregation goes wrong, instead of aggregating within each group the aggregation happens over all together, which is then displayed by group:

Is there a way to have the line graph aggregate over the categories in the by group and not the month? Either by some option in the line graph or by calculating the aggregation differently.