yea, what jeff said.
i mic at the edge of the cone, almost never in the center.
i also rotate the mic off axis, about .75" away from the edge of the cone, at about a 30 degree angle, with the element towards the center of the speaker..
then, slowly, i shift the mic, locked into it's angle, a little bit closer to the center of the speaker.
i may do this 10 times or more, before i find the sweet spot.
the EQ i want, for that particular track.
making miniscule changes in the location of the mic, is all you should ever need to dial in your tone.
the trick is, to have the patience, and be able to shift that sucker as many times as it takes.
it really helps, and in fact, is absolutely necessary, to have someone else shift the mic for you, and to be in a completely different room/location than the cabinet (ultimatly, a real studio with a sound-treated control room, and you are hearing what the mic is hearing thru your monitors.
anything less than that, is a compromise, and you are just guessing at what you are getting.