Second test using 4:1 attackers to defenders. This one was over very very quickly, due to the large amount of attackers, breakthroughs happened, which killed a lot of fortified infantry very fast.
The combat lasted 6 rounds
Attackers: 774 kills
Defenders: 367 kills
I also noticed that the attackers seemed to have an accuracy of ~0.5% whilst the defenders had an accuracy of ~10%.
That's not how the numbers work. Remember, it's a square root function; if the attackers are taking double the damage, then they need SQRT(2) times as many units to win; that's only 1.42:1 advantage.
Sorry, I'm not good enough with mathematics to understand what you're trying to say, but I trust you. The thing is, though, the attackers aren't taking double damage. Given the hit rates of fortified infantry vs non fortified infantry, they're taking ~20x as much damage.