Anyway, I just don't see
[tex] Wm = \int_v B^2 dv [/tex]
contain the informations of number of turns of each individual inductors, the surface of each inductors etc. Unless the formulas assumes all surface are same, all turns are the same. That is a big assumption.
This is the reason I still resort back to the very primitive formula with the summation of individual inductor as shown in post #5.