Strange that level 4 has been giving people problems... A small jump should definitely be short enough to avoid hitting the top. I know we don't have a visible frame rate counter so it might be hard to tell, but did you experience low frame rate? The game is slated to run at 60 FPS, so if it felt choppy I'd suggest downloading the Windows build instead. That build performed much better for me, at least, and it may help you get through some trickier sections.
Thanks for playing!