Hi!
You're right. You can only jump from flat ground, and it's an intentional design...sorry, but the game is very short and if you don't have a minimum of difficulty, the player would finish it in a few minutes ;)
But, knowing this situation, you have to follow a strategy: you just have to stop at the right point and jump from there.
Thank you very much for having tried my game and for your observation. Do not doubt that I will take it into account for future developments.