The scenario you depicted makes perfect sense, but I am afraid RadChart is not designed to support it. The chart grouping has been introduced with Bar series as target type. This is how it works - the items are grouped in series based on the value in a certain field. For pie charts multiple series would mean multiple pies (again -- unsupported scenario).
Luckily, in this case the solution is simple -- you can transform the data manually before sending it to the chart: