In your pic the assist is nearly half way down the jig..........when you lift it up by the solid ring.....it should be no more than a third down the jig (IMHO)......You said 12cm long.....go 9 or 10 at least........Personally i heat shrink.........it makes the assist stiff.......the hook stays facing out nicely and is easier for the king to suck it all in......It also provides some protection against cuda......People will argue that but i have used one assist rig all day.....the one in my pic had been beaten by kings and cuda........I never use just the cord like that but hey.....the hook size looks ok but if you can get some tuned gamakatsu 35.......they would be perfect for those jigs.

Boulder used to sell those.......Dont know if he still does.