It needs to be based almost ENTIRELY on your reliability.
Guess what, most people who don't show have almost no reliability.
To put that into perspective, I was even unhired (9 reliability/4 performance) for somebody who has a similar build, but is lower level, with 2 reliability. Their performance was just one point higher. They did not show.
What's the point in hiring a level 35 player with 8 performance when his reliability is 2 or 3?
Also, several of the people who were signed up for defense were participating in another battle about 20 mins prior to the siege, the same was true for the attackers as well.
E: And by "almost entirely" I do mean, if somebody has 10 reliability, because they show up to battles, but do nothing but grief and have low performance, they won't be hired either. Why hire somebody who IS going to be there but be detrimental to your fight? I.E. that person who had 1 performance and just built a siege tower inside the castle last round..
Re-E: I think that NPC controlled things need to have their nighttime set to every hour until :45 past. Rosters are updated 45 minutes prior to the battle, and noshows are removed, and roster updated to include players in those spots 15 minutes after the start (which would be 12 or 13 mins after the initial phase)
Re-E-E: And if a really good player (high performance) griefs for a round this should be alter their performance considerably. There are players, good players I might add, who have gone severely negative in the Almerra Castle defense. Hmm, let's see, they are fighting against a friendly faction, I wonder why they are doing poorly for once.