The subject of resistance is very subjective, I am sorry for this cheap pun.
I therefore have long hesitated before writing this page.
My mathematics background urges me to try 'definitions' first. I also really believe this to be a good idea because we might understand that we agree or disagree without exchanging the one for the other.
Definitions is in quotes because rigorous definitions of resistance and openness are impossible of course. When playing a note from piano to forte more resistance means that the forte note seemingly is played with more effort than the piano note which comes without effort. Less resistance implies that the piano note as it were has to be held back and the more forte note is the easy one. Pianissimo or fortissimo always requires effort. It will be clear immediately that there is room for taste here.
This should not be mixed up with openness or closedness. The flute should always be open in my opinion. Closedness in a flute I would characterise by the feeling of a piece of rubber being pushed over a wooden table with friction when going from piano to forte or even the piano not speaking easily. This is bad of course. The piano should always come alive with a mere whisper. The resistance should not be like rubber friction but rather like pushing against a spring. There are prominent brilliant players who are religiously convinced that resistance must be there, there are other prominent brilliant players who are of a different opinion. So you see who am I to try to discuss this subject.
I think that when people say the flute I have has so much resistance it is so difficult to play they may actually have a flute that is not open. This most likely is caused by a problem with the mouth hole. It may have nothing to do with the type of original, just with that particular copy.
Originals always, really always have the resistance such that it is in the middle. This means equally easy to go to forte and to go to piano. Because nowadays there is a wish to have the traverso louder many copies have less resistance, so one gets forte more easily but has to work for piano more then on the original. I do not think that it makes the traverso louder it just causes the forte to be there immediately. With the right technique the original with the resistance equilibrium in the middle is just as loud.
My choice is to keep the resistance like the original in the middle!
