OK, how about
average over distance d = 0 to 20 of (chance to hit at range d * damage at range d)
for direct fire only (not counting combat sensors, ecm, race bonus, etc.). One problemo would be that it favors longer range weapons, which wouldn't make sense if you are using a "point blank" style strategy.
So back to the drawing board. On the other hand, I'm happy that SEIV can't be reduced to some simple formulas
