The reason the reference axis was in contention with the Neumann was that it is very explicitly specified in the manufacturer instructions, and it is not at all an unusual location =]
General procedure is to measure at the tweeter axis unless otherwise specified.
Aren't those 2 statements in cotradiction?
Where things have sometimes gotten complicated for me is when the tweeter is placed asymmetrically on the baffle.
And what about 3-way? Also at tweeter axis or between tweeter or mid driver?