I am working on an application that uses foursquare data.
//this is the series chart that has had some delving into - but there are some bugs still running around h
I'm not sure I understand what is your problem but I've decided to try to create that chart from you screenshot with sample data from your plunker. Here is my result:
My script is making sure that smaller circle is always on top of the rage one so both circles are always visible. Here you can find my code: