I am lucky enough to own a few standards, and on the whole, they are a largely bomb proof design. They were made using exceptionally good quality steel, which means that bad wear is unusual.
The loading tap is also quite an efficient fitment that is usually pretty airtight. The loading tap on a BSA standard is secured with two screws, which hold the keyhole shaped block in place. These two screws need to be tight. There is a spring loaded plunger pushing against that plate, and if it is not absolutely tight, the tap can leak.
I wouldnt get too hung up on the tap test - with the whoosh as you describe it. Far better to make sure that you have a well lubricated leather washer in place, and a good spring (or springs, as some guns have two smaller springs in place of the one single mainspring.)
Sometimes a really good barrel clean, can both improve velocity and accuracy combined. I have occasionally discovered scored compression chambers, which can affect power, and also the main leather washer can be a bit dry, which will also have a negative affect on velocity.

BSA standards started off, with the main leather washer, and small inner washer held in place by a single flat headed screw and brass dished washer ( the large head of the screw fitting flush into the front of the dished washer), however after about 1930, the washer was held in place using a round nut, which screwed directly onto the front of the main piston shaft. These pistons were heavier and longer, and consequently a bit more power was possible.
BSA designed these guns to have the leather piston washer regularly lubricated with a few drops of oil, every few hundred shots, so I guess limited dieseling was factored into their operation. Check out Danny Garvins fabulous vintage BSA website for more info.

Regards

Lakey