You can use Power under math. And plug a vector 3 into the main material nodes World Position Offset input and raise the z value to lower the center of ur material. I have mine now set up where the ocean is at the very bottom of what unreal can do and the snow at the very top. And if u haven’t figured it out already just invert the snow function to create an ocean layer at the bottom. Oh and in order to paint i assume u have to run this through a landscape layer blend? Are you able to do that?