I think this is fundamentally correct. I would included Energy state (alt+velocity). Such that your Situational Advantage was the (sum of (enemy E-state/ENY))/(sum of (friendly E-state/ENY)) within Icon range.
Would you not then have to factor in the players comparable e state in every case. e.g I am in a high speed La5FN flying just above a furball where the enemy has a significant E (and ENY)advantage over the freindlies. Actually my SA is very good but the maths above does not show this.
Unfortunately the SA state is too dynamic (IMO) to lock into such maths ................
within a few minutes of the above I could be low, slow and being chased by 2 other La5FN's whilst 20 comrades(in La7's) are zooming down from alt too late to save me. Now my SA is pretty poor but the maths would show it to be quite favourable...............
The two examples shows the dynamic change state without a mechanism to factor into them some maths that reflect the whole mission (short of computing a running average in real time.)
Also my energy state is a matter of my ACM why should I get a bonus for putting it in a worse situation than my enemy?
Counting each enemy and each freindly to come within #yards is a simple thing............ freindlies and enemies are only counted once and the maths are done upon landing. It may not be as refined as some may wish but it does provide balance when numbers are disproportionate.
I doubt if frequent horde members are that interested in score but if any are, then (this way) they will see the normal perkage earned suffer when mingling with the horde.