I’ve seen a few posts for older versions of Blender tackling this same issue. Often their solution is to change the Normal in Velocity to 0 but for me, that just affects the scale of the rocks. All the rocks have their origin right in the middle of their mass.
So I feel like it’s down to the position of the particles in the modifier list. I put the particle system from the top to the bottom… but now they’re under the surface
You’re not exactly showing what you’re doing so we have to guess. But if you scatter the particles on a terrain mesh and then displace that mesh this is what will happen I guess.