Overall, I normally place my shield generator and then my cover shield, which works awesome because they cannot destroy it while the cover shield is in the way. Then I place the phaser turret to the left of the cover shield, (Because if you place it behind the cover shield the phaser turret cannot fire duh.
I experienced a easy bug to replicate, where the phaser turret can fire without taking damage. Please check the link below to see what I'm talking about.
As you can see, the phaser turret IS INSIDE the cover shield, and can still fire. If the turret is being aggroed, the AI stand still, and the turret can attack freely, as can you sometimes, as long as you don't pull agro from the AI (Aka doing more damage then the turret does). Thus they will always stand still, clueless, and the turret will never take damage because its behind the cover shield but because its 'IN' the cover shield, it can fire too, for some reason. Kinda like a invincibility shield while being able to fire
The easy way to replicate this is to place a cover shield, do NOT move, then place a phaser turret. You will see the turret 'levitating'... again, it can fire, but has the cover shields protection, and AI are clueless/don't know what to do other then stand around.