if i understand your math correctly, it seems like it is more of a guess as to how distance affects accuracy. not a concrete formula that makes all distances fair. so it's probably better to get scores at different distances from people and then make a graph with it that we can publish.

Are you sure that would be a linear function? Eventually, the target will visually diminish more per meter as you go to a further and further range. Also, the effects cited of elevation, windage, and precieved target surface are going to come into it at a higher rate the longer the range.
Either way it will work, I was mostly thinking of the ease of operation, and fact that the balearic system uses something similar.

The balearic system uses different distances, but the scores go up at the farther distances. Therefore, they have a similar system, if not designed for scalability.

I agree a linear function would be easier to work with. Perhaps a larger table of distances and scores would be necessary, with the formula attached for those who want to be overly precise.

The advantages to a "3/5 @ 50" system are that it relies on the diana hits first to win, then board hits for tie-breaking and more specific ranking.  However, like the Balearic system, you'd have to have a score at every distance to truely show your skill over the range continuum. But a straight point system has no respect for range: one hit on diana at 100 meters could loose to five board hits at 20, with the bull still intact.

I think that's a factor worth thinking about, since we are aiming to reward propper marksmanship, not almost-marksmanship.

No shotgunning. That defeats the purpose, unless you're shooting skeet.

Otherwise, how do these point systems deal with this issue of diana vs board?

Who's diana???