Yamaha BBNE2 settings?

Hi BBNE2 owners,

I recently started using the ‘magic box’ mid-cut circuit in the preamp. I had always kept it turned off because I didn’t understand how to use it.

Now I always keep it flipped on, especially when recording the bass directly. It can be subtle but it sounds great.

I have done some experimenting but I haven’t landed on a setting for the black knob controlling the frequency.

Can anyone share any practical advice on how they use the circuit? Mostly doing home recording now, but plan to get back on stage eventually.

Thanks!