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I am a good inch longer and much thicker under VED than when hard with Quad Mix (injection). Normal for most guys?

That was my experience.

I think part of it was that the vacuum pulled everything forward, even parts that would not be forward with a "normal" erection under any other circumstances than under a vacuum. Another explanation (I think) is that the vacuum engorges all tissues, even ones that don't have erectile capacity.

I have heard guys say that their penis is the largest they have ever seen inside a VED. It's amazing!
But then, when they remove the device, it's back to a more "normal" size.

The vacuum will force out some of your internal penis. Your dick under vacuum will be engorged more than under normal natural stimulation. In addition, the curvature of the cylinder tends to magnify the size of your dick inside the cylinder.

It pulls glans which is not what happens in an erection. It also goes deep into the pubic bone.