Depth is not that relevant. It’s a by-product, not a goal.
The goal is to imagine getting your butt as far as your face as possible. Imagine that your body is a bow trying to shoot an arrow. Your butt is the bowstring and your face is the handle. Pull the string back as far as possible and bring the handle forward.
At no point of the RDL should you actually think about going down. Touch the back wall with your butt, tough the front wall with your face/chest.
ROM will naturally limit itself depending on hamstrings flexibility.