How tight the film cone should sit in the blowpipe is to a certain extent a matter of taste. Some say that as a rule of thumb, an arrow should slip easily through the barrel. This is probably more true for the hard cones. Foil cones are very dense. For this reason, I believe that this rule of thumb does not apply here. 

I first tried to determine the correct length of my foil cone. After that, I found out for myself through the different layers how tight the film cone should sit in the blowpipe. If it sits too lightly, not enough pressure is built up and the arrow doesn't fly very far. If it's too tight, you have to blow too hard. This has a negative effect on the aiming accuracy, among other things.

The foil cones are so tight in the blowgun that I have to put a little spit in the tube before the first shot, otherwise the arrow won't slip through. In my opinion, there is no standardized specification here, everyone should find this out for themselves.

meine Variante
my variant
nicht stramm genug
too loose, not enough pressure is built up here