And, I am sure that you saw it, but I think it is worth repeating:
I would rather see the HQ that is the chain-ee have its Supply Level read as 8, 7, 6, 5, 4, 3, 2, 1, 0 as it gets further from the chain-er. This would make it easier for me to tell what is going on. As it is now, there are often many HQ's that display 5 and it is completely unclear what is going on.
When it remains at 5 the whole time it makes for a lot of counting hexes while playing.
I never see my chainee HQs going more than 4, assuming no more than 4 supply from another source
I would guess that they are not linked then as by default if they are linked they should jump to 5.