This is interesting:
if you are unable to reach shelter and you experience any of these signs, or if you otherwise feel that you are in immediate danger, assume the following position quickly:
Move your feet close together, crouch down, and grab your ankles. Tuck your head down as far as you can. Don't lie flat on the ground.
Even so, this traditionally-recommended 'crouch' position may not prevent injury from a strike (there is no evidence to support it having any effect). Again, your focus should be avoiding getting into such a situation - it's never good to have to consider using such dubious 'last resorts' to begin with.
So they recommend the crouch even though it says there is no evidence it helps. And why isn't lying on the ground good? That was my plan. Why should I change to crouching when it says there is no evidence it works?