2nd row doesn't need to drive up. But as his shoulders must be above his hips, there is an upwards angle....
If the 2nd row stays still, and the opposite prop drives forward, if the prop can't take the pressure, he bends. Try it with a bit of card against the wall if you don't believe it.
If the prop can't take the pressure, the 2nd row can (and should) go backwards, to protect his prop.
If the 2nd row stays still, and the opposite prop drives forward, if the prop can't take the pressure, he bends. Try it with a bit of card against the wall if you don't believe it.
If the prop can't take the pressure, the 2nd row can (and should) go backwards, to protect his prop.