Applying the same y axis maximum to several charts related by dataset

Hi,

I have a report which shows a main chart for the group along with four sub-charts from the same dataset only this time split by each mill within the group.

The problem is that the y axis for each sub-chart is different.

I have tried changing the y axis for the sub-charts to max(sum(value, per mill)) but it doesn't like two levels of aggregation within one formula.

Does anyone have any other ideas for a solution to this problem, please?

Thanks in advance