INSANELY late here, but the connection of the mixel ball joint on the neck should be swapped, so the part on the head is female and the part on the neck is male.
this is something to always keep in mind when using mixel joints, as it does matter with the possibility you get from it.
by having male on the head and female on the neck, you require a second ball joint in the neck to allow for effective swivel. by having it the other way round, you get head rotation and tilt up and down. you do, however, sacrifice side to side swivel, but that is the deal with mixel joints.
this is something to keep in mind at all times when mocing. "how will this decision affect the posability of my moc, as there will always be limitations inherent to the system.
for example, ALWAYS have the part of a shoulder connected to torso be a male conection (a balljoint), unless you have an arm design SPECIFICALLY built to counter the problems of having it the other way round. this especially goes for mixel balljoints which are far more limiting to poseability
sorry for rambling
(ALSO, sorry for probably stating the obvious, but its always useful to have the information written down somewhere accessible.)