Why does only one person agree with this really obvious suggestion.
I am guessing that the radius line might be the center of the edge of the effect. So say a spike from Impalement on the outer edge might be half inside and half outside, so it can still hit things outside the radius.
FYI to programmers, that's not how the radius should work. The radius should completely contain the entire effect. It doesn't do to have people supposedly outside the radius getting hit, with the exception of surface effect propagation, obviously.