You should not be using average: you should be using median (or perhaps average, using comment scores capped at 8 or 10) as the strategy you're using now will o

You should not be using average: you should be using median (or perhaps average, using comment scores capped at 8 or 10) as the strategy you're using now will overly reward comments which hit a community sweet spot and garner 100 or so points, and discourage comments on stories which have been unwisely ignored [both of which tendencies are somewhat too pronounced on the site already]).