Tubi header question flange

Has anyone had trouble tightening the y pipe flange stub onto a tubi header. I'm not sure if i got covid parts or what here. The tubi pipe OD must be a smidge smaller than oem. I have new stubs and the old neither will clamp tight onto the new tube. They measure pretty much the same but i havent put the micrometer on it. The difference has to be slight or an out of round. The old clamps are better but still not tight. Not sure if im being a dummy here or if I'm truly fighting a real issue.

 

Looking further they barely even clamp on the oem header. I think the clamps themselves are sub par and distort/stretch rather than clamp. May substitute more traditional band clamp in lieu of the oem ferrari clamps and see if that is better.

 

That's exactly what im referring to.

 

Tight there would seem important otherwise its a big exhaust leak. Even at full tight ( with the oem clamp) i can slide and wiggle the flange.