Help Koss Tank!

Hi. Good ol' Koss is my tank and he's doing alright, but I'm sure he could do better. The problem is that I need to help him do that, but I'm not sure how. The main issue is that he has trouble keeping aggro of large groups of mobs. He'll usually run up and attack someone, and the others will run around him and pummel the rest of the party. I've tried the following:

Set his flag way ahead of the rest of the party so that he aggroes the mob while we're out of aggro range. Problem: as soon as he gets within aggro range he charges at a random enemy, often a caster in the back, and all the melee enemies then charge us.

Target the closest enemy and lock his target on it. Problem: Koss won't attack the enemy on his own until we're very close to it, often so close that we're risking pulling them. He'll then charge the targeted enemy and the rest of the mob will run around him and charge us.

Please help Koss!

Flag him forward to just outside the aggro range on the mob. Then pick the target and send him in. And here comes the nub - from what I've seen. Hang back at a safe distance and wait for a little while, don't all rush in before they're all engaged with Koss.

Even better if you give him a Dervish secondary and put some points in Earth prayers, give him Veil of thorns, so by the time you get there they're all crippled and not so quick on breaking off to rush you.