I have observed your requirements and suggest you to please try using following sample code on your end to serve the purpose.
float x =TemplateChart.PlotArea.X;
float y = TemplateChart.PlotArea.Y;
I have observed the issue shared by you and have been able to reproduce the issue on my end. The returned plot area values must be between 0 and 1 as it is relative to chart position. An issue with ID SLIDESNET-38207 has been created in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be automatically notified once the issue will be fixed.
We are sorry for your inconvenience,
The issues you have found earlier (filed as SLIDESNET-38207) have been fixed in this update.