Full Body IK Stiffness Settings Questions

I have effectors on my character’s hands, head, pelvis, and feet.

I’m trying to mess with full body IK settings in my character to make the spine more rigid.

I tried excluding bones initially and it seems like the bones stay stiff in absolute space not relative space. I have similar results when giving them 100% stiffness settings.

My character’s head goes roughly where it’s supposed to but the spine seems to keep its original pose in absolute space rather than relative to the parent bones.

Like if my original pose has the character heavily leaning forward due to a crouch, but my IK rig positions the head higher up, the spine leans forward super hard while the head is detached and going where it should.

The green is how the spine should be angled, and the red is how the spine would be angled in the original pose.

I have this system that helps repose my character so the spine pose is preserved while moving the pelvis to a different location so the head is where the eyes are, which is great for first person. There are also some planes that constrain the final location of the pelvis so it’s not too goofy looking, and the pelvis essentially rotates around the head. This way the character animations are roughly preserved but deformed to match the eyes location and even helps when looking down in first person view. This system also works flawlessly in my previous non full body IK setup but I thought I’d try out full body IK instead of using 2Bone IK for arms and legs.

This is how it should look when it all works, only here I’m not using full body IK. It’s instead doing 2 Bone IK on each limb and repositioning the pelvis around the head transform while keeping the eye transform for the head.