If you want to do what we mean, then your fort must be full of archers Radooo...
Anyway... everything depends on other factors. Mil med, fortification, number of trebs... They all affect...
At the end of era there will be lot of players with 800 trebs
and excess of archers are not so useful
And I don't think that it's so much to win 2 more points during the fortress siege