Tail Rotor Balancing

[Geno Mancini]

I'm going to be checking the tail rotor for balance.
I position the accelerometer vertically on the bottom of the gear box pointing up.
I do this because I think the tail rotor and tail boom move in the vertical direction a lot more than the for/aft direction.
Also the main rotor blades might be moving the tail rotor up and down somewhat also.
As a thought, you probably should have 0 pitch on the main blades before taking a tail rotor reading.
Dyna vibe shows the accelerometer mounted in the for/aft position, pointing forward.
I believe these accelerometers sense movement in the longitudinal axis, (from bolt mount to cable exit).
So, wouldn't you think mounting the accelerometer vertically would give you a better reading of tail rotor imbalance?

Any thoughts on accelerometer position and why?