Sprites with custom depth map

I’m trying to port my game from unity to unreal. The game has fixed isometric camera with 3D stuff a 2D sprites.

Each sprite has normal texture and “depth map” texture, that is the position of each pixel in a local space encoded as float image. Now I need to make a shader to write to depth buffer for each pixel from the texture. In Unity I have made a custom shader that wrote to SV_DEPTH. I’ve seen that there is “Pixel Depth Offset” but the documentation is sparse. What bothers me is the word “offset”. Cut the depth value be any value or it needs to be +/- relative to the current depth? I could post the relevant shader code from unity if needed.