New User of the Month Algorithm Questions

This is a very good point and I agree with you that the current algorithm might be too simplistic. I think a good first step would be to make the post factor nonlinear like

SUM(...) / SQRT(5 + COUNT(DISTINCT p.id))::float AS score

or maybe even

LN(1 + SUM(CASE ... END)) / (5 + COUNT(DISTINCT p.id))::float AS score