Terrain Brush size to map size problem

Ok to make this simple il try and explain everything

I made my first map terrain (300x300) and did all my mountains and that and looked good, now I made another terrain for my 2nd scene and made this one 300x800.

My problem is my paint brush looks square (set to scale 1) but comes out more like a 1x3 rectangle. so it looks like its a scale of 1 form 300x800 square

Is there anyway to fix this, I have already set up my mountains but if I have to start again I would cause these maps need to be the same texture