I would also like to know how to override the article SEO title just by text (not a field value). In fact, I would like to build the article titles from a custom text plus a field value. The situation is even more unclear as there are now 2 fields for overriding the title in the content type config ( see this topic).
It would be nice if anyone can bring light into this
I did not find a solution to this, but from reading a lot of forum posts it seems it's not possible to setTitle with the Joomla API at all. The code is added, but the original title tag from Joomla is still set, and higher. So.. just dosn't work out well.