The whole purpose of the nipple is for a car lift. You plug all 4 in, they stay put and move the arms under the pucks. Makes it easy to spot and makes the arms clear the battery.I know it's probably unlikely to happen, but what if the car starts to shift sideways? What's to prevent it from happening if the puck is not "plugged into" the car's chassis without the nipple?
Some “pucks” are magnetic and flat.
They are not meant for sideways grip. Although it certainly won’t hurt. Anything that puts the load in that area without gouging up the area around it is probably fine. Common sense applies as far as slipping goes.