Yep, sounds right.
You might try and set output at Fb (tuning frequency) because it's usually the lowest impedance the amplifier will see, since 50Hz will be in the area where the impedance peaks are higher on either side of Fb. I'm sure that the actual impedance at Fb will also be higher than 1 ohm so you will need to factor that in when you work the formula. Does PK have the impedance plot for that enclosure workup? Maybe he can quote the actual impedance at Fb for you.
You might try and set output at Fb (tuning frequency) because it's usually the lowest impedance the amplifier will see, since 50Hz will be in the area where the impedance peaks are higher on either side of Fb. I'm sure that the actual impedance at Fb will also be higher than 1 ohm so you will need to factor that in when you work the formula. Does PK have the impedance plot for that enclosure workup? Maybe he can quote the actual impedance at Fb for you.