[Dialog] Is there a way to auto position & size the composition window by default?

I haven't messed with the Dialog setup in years.
 Dialog: Settings > Layout

But every time I hit "f" to followup to an article, the composition window
that pops up takes up the entire monitor width and height.

Of course I can manually re-size & re-position the followup popup window to
be only the left half of the monitor screen width (and full height), but
then the next time I hit "f" to reply to an article, the composition window
that pops up above the Dialog GUI still takes up the full monitor again.

There must be a way to set the composition window size & location, isn't
there? I just want the composition window to take up the left half of the
monitor width at the full monitor height.

How do I automatically position the composition window to half the monitor?