masked opacity is a binary function. the pixel is whether solid or transparent. the threshold in the material settings is the factor where this “binary line” is. to get a gradient you’d have to use dithering. i tried to make clouds with that too. it looks pretty gnarly, means bad. you can try yourself and decide if you want that.
the other options you have are translucent material clouds and being careful how many layers you have. or you paint a stylized sky box texture.
that’s my take.