this because you use plugin l4d2_ai_damagefix that got value from cvar z_pounce_damage_interrupt in coop this 50 (in versus 150 see https://developer.valvesoftware.com/wiki/L4D2_Gamemodes_File search by z_pounce_damage_interrupt, you see that coop not change default value, but versus change to 150)
because this you should do 50 dmg for hunter to skeet him, it very easy!
please add in config increase z_pounce_damage_interrupt minimum for 150.
this because you use plugin l4d2_ai_damagefix that got value from cvar z_pounce_damage_interrupt in coop this 50 (in versus 150 see https://developer.valvesoftware.com/wiki/L4D2_Gamemodes_File search by z_pounce_damage_interrupt, you see that coop not change default value, but versus change to 150)
because this you should do 50 dmg for hunter to skeet him, it very easy!
please add in config increase z_pounce_damage_interrupt minimum for 150.