Keeping your heels down is by far one of the most important things when it comes to getting a good position. It's about distributing your weight right. Yet you're not supposed to push your heels down as far as you get them; you're supposed to put the weight on your stirrups. Don't let your legs slip behind or forward! There's supposed to be a line between your heels and your hips. By doing this, you'll get a lot more balanced.
How much you're gonna lean forward depends on the height of the obstacle. If it's a small obstacle (ex 1m) you don't have to lean that much forward. But as you keep on jumping and working with your position, you'll do it automatically :)
Hope this helped you somehow!😌