Grease pencil: Masking meld issues

I want to try something different.

I drew a body object and want the shoulder to blend with the body and arm. I tried masking, but that’s not what I want. I can still see the shoulder line inside the body. I want its line to be invisible inside the body. And the line to show on the outside of the body.

testtsIt works like this.

How do I fix this? Don’t forget the images or GIFs.