What is the best way to display a Line Chart with predefined values for different categories?

My chart is displaying tasks by type for a certain team. Using another model that takes the count of tasks and divides it by the countdistinct of created by I was able to get a rough estimate of the “average” for each category (first chart). Is there a way to create this line using pre-define minimums instead of a UI formula field?

An example would be AE Connect = 20, Call = 250 etc. I’ve tried using the info found here: http://api.highcharts.com/highcharts/yAxis.plotLines but can’t seem to get it working.

Any help is appreciated.