I doubt that there are any daggerboards that move aft when you hit something. centerboards do that, and that is the main reason that the Tornado has centerboards instead of daggerboards.
the top of a daggerboard is cut back so that when they are up, there won't be a sharp trailing edge staring you in the face. should you hit that trailing edge with some part of your body injury is likely. the hobie 18 daggerboards have lovely curves. The curve on top, on the aft edge is for this safety factor. The curve of the leading edge under water does allow the boat to ride up on them (somewhat) should you beach with them down. This means the boards must be somewhat wider to get the needed area which inturn gives them a lower aspect ratio and less effcient lift. It was a compromise for safety and usability for surf sailors.
hope this helps