Remember, more than most, Empire is an army that thrives on combined Arms tactics.
Steamtank draws fire, and is not driven back, so it is nice to position it to force shooters to attack it, instead of softer targets.
Steamtank positioning is pretty flexible so it allows you to pick your targets of opportunity
Shooting-driveback rules on enemy dictate the driveback from the nearest shooter, NOT the nearest HITTER, so the extra cannon + a well positioned wizard can cause crucial confusion.
Just remember that (as in Real Life) the steamtank benifits from an escort. Use the Empire version of the Trollslayer BBQ....