Unfortunately not. We only have the 2 options inside the booking page settings:
update only the iframe (the child iframe or “C”)
or update the whole browser window (“A”).
There are ways with javascript to redirect only the direct parent with the “window.parent” property (or in html with a script tag and the “window.parent.location.href” property), but for that the child and parent need to be on the same domain, which is not the case.
Thank you much. I did find a way around it using my own JavaScript programming. I have the YCBM page go to a known fixed page on my side, with a query string value that I set. On that page it triggers the parent page, which is doubly easy because they are on the same domain, and the PostMessage command works without issue.