Single v. Double "Return"

I enter and edit most of my posts in Ulysses App (Apple), and, though Markdown, it treats “Return” and double return differently than markdown, making a simple cut/paste of text from Ulysses to require an awkward look through to ensure that non-first paragraphs under a heading or subheading have a second “return” so they are properly spaced. Is there a way to make the behaviors parallel? I need to leave Ulysses set as is because that works with my book publishing app (Vellum).