You can do even better with the manual correction since that permits you to move the filters in frequency and Q, neither of which is done with the AutoEQ.
I'm no expert but a true null is a phase cancellation of the signal. That's where one wavelength in phase cancels another wavelength 180 degrees out of phase. Changing the volume will not eliminate this null. So the way you get rid of it is to change the phase of the original signal and that will move the interference point to somewhere else in the room.
I listen in the near field and my chair is fixed in one position so I can't answer your question as far as it applies to the SMS-1 in my room, I just don't move around the room during critical listening. My guess is that it will sound about right anywhere in the room except when you are near a room boundary (In a corner or against the wall). These are really long wavelengths we are dealing with so there may be dropouts in certain places in the room but I wouldn't think position would be all that critical.
My tweeters on the other hand require a very precise listening position.