ok think of the weighting of the spring like a gradient, the top loop is weighted 100% to the top bone and 0% to the bottom bone, the next loop is weighted 90% to the top bone and 10% to the bottom bone , … , the bottom loop is 0% to the top bone and 100% to the bottom bone.
side note might be outdated but each vertex can be weighted to 4 bones which total to 100%