That was just a quick test, - did have about a 5mm spacer on it, but the one I did for the plane had about 30mm. Depends a lot on how thin the material is as well and you have to allow for trimming. .5 mm would have gone around a lot better. You also have to have holes through the plug as well so it pulls around the plug.
The CKD furniture company I worked for (largest in the South Pacific) pioneered round edge vinyl covered table tops in NZ using a big German press which they modified. Germans said the thin Vinyl that the company wanted to use would not work,- took them a year of experimenting and proved them wrong. Machine used a large silicone blanket and oil heated platen.

Probably one of the reasons Red, also they were apparently trying to compete in a saturated market after the war. They upgraded the motor a number of times (as you would have seen) and a few other mods but couldn't compete, - pity as it could have been a ripper little plane, better looking than a lot of others and faster.
As you said, tandem is not conducive to families, and a lot of companies were advertising their 4 seaters as an extension of the family car. Gone a bit the opposite these days, not many making small planes now, mainly the Chinese, (probably count them on 1 hand now) The Streak would probably fit in the sport plane class these days.