I have a dui cf200. How I’ve been taught and it’s worked for me is when you are wearing the suit on land the neck seal should not feel comfortable. It should be tight. Once you get I to the water you should be fine. Plus take into fact that when the water is cold your neck will shrink some. If rather have a right seal rather then a seal that when I try to fill my suit and look down I have air blowing out from the back of my head and water getting in.