Possibly one must consider the Planck distance implication when trying to resolve this problem. At the Planck scale, the distance dimension breaks down, or rather reaches a limit to where distance can no longer be classically reduced or "cut in half". One would then have to travel "around" that last infinitesimily small Planck distance unit, something which we do every day when we or anything else in our macro world engages in motion. Otherwise, we could never move at all. This movement, then, would of necessity require travelling through a much smaller 5th,6th,7th., etc., dimension, something which at present is theoretical, but which is nevertheless considered viable in string theory and other multi-dimensional theories. In short, you WILL eventually reach the source of the magnetic field, and then the limit to its power will also be reached.