Showing HTMLFlow in Window

Hello!

I need to show piece of HTML (in fact it's just formatted text) in modal window (Window class).
I use HTMLFlow for this task and autoSize = true for Window.
Size of HTML in HTMLFlow can be different, but at all I'd want to
a) keep Window from scrolling
b) preserve (if it's possible to do without scrolling) desired aspect ratio of Window/HTMLFlow. Or set preferred directions of expansion to HTMLFlow (it should expand at first in horizontal)

How can I do it? Of course, I don't want to specify window size exactly, because of different sizes of HTMLFlow content.

Thank you