It isn't easy to get good proportions for a model, especially at this one. I had a look at the field model of your rework and [CleverNameHere] is right it's much too short. He is flying over the ground. The models I create have usually the feet in the ground - it's a disadvantage, but it's needed for right proportions.
You will get problems with some animations, some parts doesn't have the same direction as they bones and others need to be more central to the bone.
In particular the hip-chest bone should be longer, so the head could be closer to the joint.
(To be honest it happened to me lately with the APZ Cloud field model I have reworked. I have made a mistake to the upperarms and didn't followed the arm bone direction correctly, because I didn't want to make the collar-chest bones even shorter. Bad decision of me.)
However you need to make the collar bones shorter, they usually are responsible for the 'flying arms'.
Hmph, the left arm of my model is a bit too long... Anyway, I'm glad to see some more people are working with kimera at the models.
By the way the Red XIII field model by Kela51 needs some rework. I strongly recommend to use my Red XIII version as basic, because I have tweaked the bones as best I could to look best with the most animations.