The RadChart does not provide the functionality you require out-of-the-box, but nevertheless, it can be achieved. To do this you will need to supply reversed Y values to the chart and to manually replace the Y axis labels. In order to replace the Y axis labels safely, it would be best if you set manual range.
To help you get started, I have created a small project to demonstrate a sample solution. You can find this project attached below.
I hope this helps.