I think about this every day. I've really had to examine my strike so I can do honest comparisons of my banjos I make. My index finger hits the string at about a 30 degree angle, going slightly into the skin. The most important discovery I made was to hit the string like you would hit a drum, with somewhat of an oblique strike. This way I feel like I'm not going into the string (choking the sound), but coming off it. And this produces a clearer note and prevents the "Phht" sound or the 'clucking' sound. This works for my fingernails, which are medium size I guess and kind of rounded. Is that what you mean?