How is it irrelevent if say you flexed at the top of the mogul-we'll say perfect absorption so no speed reduction, then maintained that and dropped to the flat zone? Would you not speed up falling before you hit bottom? Or are you saying it's the same amount since if you extend you accelerate down slope, and if you drop you fall to the center of the earth?
Edit: I see Ghost is explaining it.
Yes, you speed up by falling, but if you hit e.g. a horizontal patch the perpendicular-to-the slope (vertical in this case) component of the velocity will disappear in the non-elastic impact. The same happens (perpendicular-to-the-slope component (now not vertical) disappears) if the patch is not horizontal, but it is not as obvious perhaps.