The advice seems to have changed over time. Back when I was young, the prevailing advice was to look for a hollow of some kind and lie down. So You made me curious, and it seems that these days, the advice is to crouch but not lie down.

I wonder about how they determined the difference, but maybe there's some body of experience. Either way, riders have to decide when to run and when to stay. For my part, where I live and ride, I can always find decent protection within running distance, so I don't have to think about defending against a clear field strike.