bullet skimmer placement

[arnprior]

Hoping someone could clarify this issue for me.I have a bullet one skimmer by precision marine.Now the company states you should have your output above the normal running water line in your sump.The place where I purchased it tells me in-sump directly on the bottom.I am currently using a mag12 on the skimmer and it constantly is acting up and not really producing any skimmate.Could other bullet skimmer users please tell me where theirs is placed and if they have a gate valve on the output? Thanks in advance.