How do I stop my Aplha Brush from pixilating?

Hi all,

I really need some help, I have created a landscape which has the settings in the screenshot attached. The alpha brush I made (which is 256px x 256px) is really pixilating when trying to paint onto the landscape. It seems the smaller the brush size the more pixilated it becomes. Which I don’t understand as surely it should be the opposite? This is shown in the second screenshot attached.

Why is this and how do I fix it? I am fairly new to UE5 so any help would be extremely appriciated!

Thank you so much!