I have an easier system, more luck oriented too as you as the bombarded do not get to choose how to take your casualties.
The defender lays out his forces in their trenches or pillboxes or even in the open. The scenario decides if the opening barrage is very heavy (use D6) or standard (use d10).
Now the attacker is going to roll one die for each squad or MG or artillery piece of the defenders. He just points to each one first then rolls.
If heavy barrage: 1-2: Stand eliminated if in open
1: Stand eliminated even if in
cover.
If standard barrage use same numbers but remember you are only rolling a d10 not a d6 so it will not be as effective.
You can play around with this easily enough – maybe the defenders have a particularly thick bunker so instead roll a d20 and only that 1 will knock it out. 5% chance.
Funny true story once – one of our guys brought his young daughter along and he was rolling dice to knock out enemy units in the opening bombardment.
He wasn't doing that well even with his D6 rolls. Well, it was the time now to roll to knock out this critical heavy pillbox on the ridgeline which commanded the open ground below. So he turned to his little girl and handed her the 20 sider.
She duly made her only roll of the night (she really had no clue what all this was about other than daddy wanted her to throw it on the table). Sure enough – ' 1 '.
The defending player's look on his face was hilarious, we all were laughing so much.