As we sometimes say here in the South "How do it know?"
I have done a number of 2 ways and MTMs, and setting 3 dB of BSC is trivial,
but for 3 ways, it's much tougher, because the Fc is in the middle of BSC territory.
Working on a 3 way with an RS270 woofer crossing to a dome mid around 800 Hz.
By ear, bass is good, but not great - think maybe I'll need to dial another 1 dB of BSC.
Here is close miked FR for the driver raw, and then with the proto crossover of
3.5mH and 660uF 2nd order.
What do you think (and what is your decision point) - is this about 3 dB of BSC?