You could look at it as early "health and safety", To make it safer after the fall they put the stones that had fallen back into the ground a little deeper, Therefore making it a little lower. It also had the desired [to the repairers] effect of making the capstone level and more table like, This was seen as making it more aesthetic [ha], This drawing from before the collapse also shows 4 uprights [but only 3 touching the stone though] - http://en.wikipedia.org/wiki/File:Lanyonquoitborlase.jpg
Something is not right. This message is just to keep things from messing up down the road