Also the math you are using is calculating the g-force of forward acceleration... NOT the direct outward g-force from the center of the axis, which is what we're really talking about.
Another simple way to think about is:
If you tape one nickle near the center of a bike wheel and another nickle on the outer rim of the wheel and then start to spin it... which one would fly off first? The one furthest from the axis.
if you're turning this into an engineering problem, then you have to look into moment of inertia to understand why a shorter lines would create a lot more g-force, the moment of inertia grows exponentially with the distance away from the center, so a parachute with longer lines has a much harder time spinning someone around it's axis then a one with shorter lines. So smaller parachutes are capable of spinning someone at much higher rotational speed which translates into higher g-forces