Progressive refinements of the current sources in magnetic vector potential finite element formulations are done with a subproblem method. The sources are first considered via magnetomotive force or Biot-Savart models up to their volume finite element models, from statics to dynamics. A novel way to define the source fields is proposed to lighten the computational efforts, via the conversion of the common volume sources to surface sources, with no need of any pre-resolution. Accuracy improvements can then be obtained for local currents and fields, and global quantities, i.e., inductances, resistances, Joule losses and forces.