an air bag assembly utilizing a releasable anchoring structure operatively connected to one or more extendible tethering elements and providing adjustable cushion depth . a displaceable support element selectively engages or disengages the anchoring structure during operation of the vehicle taking into account steady - state inputs such as vehicle velocity , occupant size , seating position , and seat - belt use . the displaceable support element may be automatically engaged or disengaged from the anchoring structure as occupant and / or driving conditions change prior to actual air bag deployment .