Normal mipmapping problem

My game is a top-down shooter. As I move through the level, the normal mapping of the ground makes quite a noticeable artifacting, with a horizontal line separating crisp ground below it with slightly blurred ground above the line. You can see this line in the pic below.

I’ve noticed if I turn off mipmapping of the ground texture’s normal map, I don’t have this issue. However I need mipmapping on the normal maps (otherwise the normal mapping becomes all pixelated).

I don’t care if the ground is either crisp or blurred, but I don’t want a noticeable half and half on screen. Is this fixable?

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There is an option on the mipmap settings where you can add fade out. I think you will find playing with that setting helpful.