I think you all (except radzmar) didn't caught the point. He don't want to know, how the "auto-text-size" works. That's what he knows.
He want to know, wether there is any possiblity to change the default font size, before LCD starts to shrink.
Example: You want to have similar pages with the same font size (e.g. 8pt -> not 12pt as it is), but if any page's space isn't sufficient, he wants to auto-shrink the text until it fits.
The easy answer would be no, as radzmar said before.