Solenoid's field intensity calculation dependency on width/diameter of coil?
You are embarking on a complex problem for which fea was developed. The coil alone will not give an accurate result. The entire magnetic circuit path (loop) must be described. In short; you must find the total iron length, iron area, air gap area and gap-length, an equation describing H vs. B of the iron, and the coil amp-turns. Then compute the total amp-turns drops in the magnetic circuit by starting with an arbitrary value for flux. If NI drop totals are higher than the coil NI, then lower the flux (many iterations may be required). When the true flux value is thus found, compute the air gap energy (the air gap NI x flux/2). Now you must rotate the armature slightly which changes the air gap overlap area and compute it all again. The difference in air gap energy for the two conditions is the energy of rotation (torque x radian angle). Solve for torque.