QUESTION? How to use blender brush on a scaled up surface?

I am tying to make a scene with a city that sits on a hill. However I have stretched the flat plane to 10km X 8km and when ever I try to raise the land with the built in blender brush it works on the first press but if I try to do it again it doesn’t overlap. I want it to adjust the raised land and the land that hasn’t been touched yet. Does anyone know how to fix this. Thanks

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