discplacement and texture for 3d terrain

Hello, I am tasked with created a simulation scene in a muddy field.  I am asking the generative fill and expand to create, starting at 500 pixels, a simple muddy and grass patch, enough resoltion to be pleasant on the eyes standing at ground level in vr.  However the size for the simulation is prob around 100 meters, I am pulling out the gen expand and can get some good results but at around 4k the new tarrain is confused and a low res blur.  I plan to have multiple 4k images to create the 100 meter environment. Any tips, as this seems an amazing way to create detailed terrain for ingame environments.

ty