In my opinion, Area Defense mode only makes sense, if you have the range and the rate of fire to be able to engage a salvo twice, if, for example, you can hit them at 180.000km and again at 40.000km.
Otherwise, the increased to-hit-probability of the (very) short range from final defensive fire far outweighs any possible benefit from long-range pd fire.
Note: If you want to use your lasers/railguns/mesons in area defense, I think it would be necessary to use a rather long-ranged firecon, to enhance to-hit chances at long range.
Example:
Using a 180.000km range laser and a 180.000km max-range / 16.000km/s tracking speed firecon trying to hit a 32.000km/s missile at 90.000km gives you a 25% chance of a hit (50% for range * 50% for tracking speed)
If you want the same chance to hit out to 180.000km, you´d need a max-range 360.000km firecon.
I haven´t calculated the mass requirements, but I am pretty sure you could put two short range turrets + fircons for each dingle long-ranged + firecon on your ship, and, frankly, I´d take the two turrets anytime.