A stack of a single poisoner probably does only 1 damage because of their ranged penalty which cuts ranged damage in half and the things you're shooting at are out of range, which cuts the remaining damage again in half.
Poison damage depends on the number of poisoners in your stack, so a stack of a single poisoner will always poison for 1 damage, 2 poisoners will poison for 2 damage and so on. And poison indead doesn't stack. |