What is the reasoning behind dividing sigma by 2.5 when performing edge validation?

[MrZander]

The paper states that ED works best with sigma = 1, which I can see is what is used.
But, why then does the code divide the original sigma by 2.5 and re-smooth the image?

ED_Lib/EDPF.cpp

Line 20 in 6ea56f1

sigma /= 2.5;

I don't see any rational for this in the paper, am I missing something? Does this produce better validation results?