miniVAP aren't glass blowers, so when it comes to the glass connectors themselves, they are 3d party re-sellers. The adapter itself is just a generic 14mm whip connector, it is possible that the glass wholesaler they get them from substituted "the next closest thing" when they ran out of glass with the correct stem width and they received a batch of the wrong ones.
The one in your photo does indeed look chunky.
I'm actually waiting on a couple of them, but it'll be a week or so until they get here. I cracked my first one after letting it get overly friendly with a huge hydratube.
In the meantime maybe try sticking the stem of the one they sent you into the business end of a flexicone+, I KNOW those will stretch to that size since I had to McGyver myself a temporary WPA using a chopped-off flexicone+ and a run-of-the-mill 14mm whip connector with a much fatter stem: