[mathematician]

how about n alliance members contributing to score, but each member contributes only the alliance average score?

So the formula is
alliance_score := min(allianze_size, n) * alliance_average_score
with n = 40 or whatever

where alliance_average_score is calculated from all members except the lowest (say) 10% scorewise (those are most likely scanners)

Examples with limit = 40:
alliance with less than 10 members => score = sum of all members
alliance with 10 members => score = 10*(top 9 average)
alliance with 20 members => score = 20*(top 18 average)
alliance with 30 members => score = 30*(top 27 average)
alliance with 40 members => score = 40*(top 36 average)
alliance with 50 members => score = 40*(top 45 average)
alliance with 60 members => score = 40*(top 54 average)