Yes, no fixed sigmoidal would have the effect I assumed was his intent.

You could set a very steep sigmoidal filter that just catches the modal region of the pdf, but that's clunky, and you have to have exactly the right filter for the particular distribution.

A simpler way to achieve "sharpening" a non-uniform probability distribution (making the modal region even more likely to pay off) is to raise it to some power >1, then renormalize.