Unfortunately, a known problem: [Output Generation] Failure of arrowhead and arrowtail to respect penwidth (#372) · Issues · graphviz / graphviz · GitLab and Allign node's stroke with end of the arrow's path width
p.s. would you please share your source again, but use “pre-formatted text” </> button, instead of blockquote. When I copy/paste, I get lots of non-printable chars.