There's absolutely no in game settings or dosbox config file.
The game fills my 16:10 monitor cutting off 30% of the lower screen.
Any fix for this?

Try asking over at the Pax Imperia subforum, you'll get more people who play the game there. :)

Normally I use those forums but no one seems to reply.
As example check out the forum for A Fistful of Gun...convo going on there now for about a week concerning an
update that GOG never added with no resolution as of yet - I had to get a Steam key from the dev.

The game was never released on DOS, so it doesn't have a DOSBox config file. As for the options, they are apparently in-game. While playing, press ESC. For more info, you might want to check page 21 of the manual.