A couple of suggestions in one...

Please add interactivity between RadPivotGrid and HTMLChart similar to pivot charts in MS Excel - making the filters and selections. update both the chart and the pivot table.  It will also be helpful if you can add splicers similar to PowerPivot.

When you click on the chart, it opens a popup menu, relative to that area - where you can select to filter that axis or value in a series, change the aggregate calculation for that value (sum, count, average, etc.), change date ranges on a date axis - like, date range picker, by year, fiscal, quarter, week, etc. 

Thanks,

Vermaak