Pink noise to amp turned up just enough that you can hear it.
Mic at centre of cone then mic pre gained up and sent to ath-m50 headphones.
Got in front of cab and moved mic away from the centre just past first "tone" change away from the high harshness then moved mic away from cab until least amount of ssshhhhh in the high frequencies. Ended up just outside dustcap about 2 inches off grill cloth.
I always mic a cab like this.
Pink noise takes away any other variables and makes it easy once you have done it this way enough times.