If works fine for all attributes of an agent by enabling the "gather data" option.
However I am not able to display the attributes of the highest model level in the same matter (not the attributes of an agent). Is this not possible or how can I display them?
Do you mean that if you set an attribute at the model level (i.e. "Epidemic") and set the "gather data" value to true, that that statistic is not available in the chart customizer? If that's the case, then that is a bug, please file a report.