Puzzled by Polycentric Distribution

     I am conducting a research on visualizing different minutes walk from the designative parks to residential buildings like the figure below. I hope the minute gradients are 5min, 10min, 15min and 20min. Whether the battery of polycentric distribution can work for this issue.  

     For further understanding of the polycentric distribution. I have another questions about it: Q1 showed in the figure below,  the function of the total amount is? When I slide it, no changes happen in the graph on Rhino; Q2, the whole distribution says distant decay distribution, so is the DP (showed by NO. 2 in the figure below) standard deviation? Q3,  how to work out the list of numbers in the legend (showed by NO. 3 in the figure below), what is the relationship between the total amount and them?