We don't use a leather flap at all. We attach a disc of rubber to the end face with a dot of superglue. Easy and quick to do, very reliable and quiet, long lasting. We have also reduced the length of our standard blowpipe by 30mm, making up the difference with a longer bellows hose. This is more comfortable particularly for smaller players. I guess historically the length of the bellows hose was limited by the tendancy to collapse when made from leather (yes, I know about the business of putting a spring inside), which doesn't apply to modern tubing.
Of course, if I was making a replica,I would go with the original very elegant pattern as shown in the photos.
Cheers
Richard