Hi!
The breasts should follow the clavicle to some degree yes, because pectoralis major and pectoralis minor (muscles beneath the breast) are both attatched to the clavicle.
I would have it follow a little less than it is now, since those muscles are also connected to the rib cage and the breast is mostly fat-tissue which tends to slide on the muscle rather than strickly follow it. But thats personal preference, depending on the character what you have now can be totally fine, just try some different values and see what feels right for the character.
But you also seem to have an orientation issue, when you move the clavicle backwards the breast moves forward and vise versa and when you rotate it around the main axis the breast control seems to rotate vertically. You need to make sure that the breast control or the group above the breast control that you are constraining is oriented in the same directions as the clavicle control.
I hope this helps!
