What level of losses?

[Fulcrum]

Right, nice tip, but is the artillery in a direct fire role open to casualties when it is directly involved in the combat? And what happens if the attack burns the last of the turn and the artillery and the supporting units are open to counter attack? Would the minimize losses supporting units retreat first leaving the ignore losses arty unit to suffer the brunt of the counter attack?

Artillery in direct attack supporting an attack can suffer counterbattery fire.
If the turn burn suddenly I suppose that your artillery units (now in mobile status) have some safe hexs of distance from the front line. the enemy woud have to overrun your units with minimal looses in the front first.
But i think that is rare. Normally you can attack in the way that I said several rounds in the turn. When the turn is with 50 or 40 per cent, is better to dig your artillery units to support your defense in the enemy turn