What kind of approaches are used in order to estimate average size of LD block using LD-decay plot?

Question

[rimgubaev]

I wonder if someone could give examples of how one could estimate the average size of LD block by looking at LD decay plot like one attached. I know that it is possible to set a certain threshold for r², but it is not clear which value should be used then. For example, I just pick r² equal to 0.3 and get the size of a block approximately equal to 500kb by looking at LOESS curve, are my assumptions correct then? Or there are other approaches to pick the r² by analysing plot to determine LD block size?