There is no secret code or a handshake to make it to work. All you have to do is check the Auto-Height and set scroll to No.
If it doesn't work after that, there must be an unusual issue going on with your page. If you provide me with a url, I can try looking into it.
Anyone who has this issue should understand that Autoheight Javascript code relies on the source page to be in correct state and format for the size to be properly determined. So, for example, if your source page is going to lazy-load some parts of the page, it'll cause issues. We will look into creating some mechanisms taht coujld determine such a change... But, at this point, it's a "limitation" to deal with.