Shock cords don't make the chain any shorter.
If it's long enough to need shock cords to keep it off the ground, it's too long to safely do its job in the event of a disconnect.
Twisting the chain does make it functionally shorter, but compromises its design strength to a degree.
The "right" answer is to make the chain the proper length, but that is not so easily done if you are using multiple vehicles with vastly different chain length requirements. You can cut and cut and cut a chain but it will never get any longer. Sure you can use a double clevis to add length, but then you're fiddle-farting around with six cotter keys and six pins every time you switch vehicles.