[userbinator]

It also looks like you'd want to avoid flapping into the top of the pipe.

[kenferry]

Perhaps I should have said "threshold_height".

    threshold_height = bottom_of_pipe_height + 10 pixels; // or something

    if (current_height < threshold_height)
      flap
    else
      don't flap

If you never flap when above the threshold, you will not hit the top.