Like many others, I hate OOB amphibious landings. I’d tweak your idea by making the attacker establish a beachhead (at least 1 defender casualty post any bombardment) before the artillery can attack and before tanks regain normal combat power. If the attacker misses on all his rolls in the first round, why should the attacker benefit in the 2nd round with increased firepower when none of the defenders were taken as casualties? How did the defender lose ground to setup artillery, etc.?