After getting some amazing feedback from Susan and Lipin, I have updated my bog to have more depth and more solid ground planes. I looked at some great references I was recommended, especially Sky the game which Susan suggested. I’d never known about ground planes before (or done a whole lot of landscape work in general) so this was really interesting to learn about.
First I tried to break down the ground planes in my shot to understand what was happening. I realized after doing this that everything looked very clunky and unappealing. I then looked at a screenshot from Sky and tried to break the image down in the same way- to work on understanding how ground planes work and how they could vary in number and shape in a scene. This was a really beneficial exercise and I saw where I was going wrong. My first attempt at fixing my planes looked way too round and gave the impression that the shot was really hilly, so I looked at various landscape paintings and my reference photos of the moors to see how things flattened out. This was progress, but I was still having some issues with balance in the image and how my characters would fit into this scene. Susan helped me here with an illustration that made things much clearer and also made me notice some other things about my shot that could be tweaked to improve it, such as the angles of the rocks.