Consider i have two armatures side by side (different X values in Object mode), both armatures are in rest pose. Additionally the right armature (see image) has an additional Origin bone at <0,0,0> in Armature space, while the left armature is rotated and scaled in Object mode such that both armatures have about the same size and orientation in the scene.
for clarity i created a minimal setup as a demo blend file. I have not found a way to directly attach the file here, so please apologize that i use pasteall.org as a workaround:
Also note, that the original scenario has got animations assigned to the animating rig, so trying to fix this by applying scale in object mode would destroy the animations.
So, here is the situation before i add any constraints:
Now i add a location bone constraint to the Pelvis bone (here named COG, center of gravity bone) of the right armature using the corresponding Pelvis bone of the left armature as the target bone. I expect that the two armatures get aligned to the location of the targeted Pelvis bone. And indeed that happens:
Remember that both armatures are in restpose. When i now enable the Offset option, then i see the owner armature moves back to where it came from, but it gets an additional offset from the target pose bone, namely the distance from the bone.head to the ground floor (z=0):
However, what i really want to get is the offset relative to the target bone's restpose, which would be <0,0,0> when the target armature (on the left) is in restpose. Of course i can move the driven pose bone on the right side down to the desired position as a workaround. But what is the correct approach to achieve a relative location movement for the two bones without the additional restpose offset, such that both rigs are animated side by side ?