I thought the same thing till I got a Ninja. With only 0.5mm of shims the Ninja head clearance is over 0.40". It depends on the head design. The Ninja head obviously has a smaller combustion chamber than a Nova Rossi, so they have to raise the bottom of the button to keep the compression in check.
For most Nova Rossi engines flack is right........ around 0.024- 0.030" of clearance is pretty good.
For the OS I have no idea
If it was designed to run on 15%-20% fuel, I'd add at least 0.2mm of shims and check for detonation after a tank or so. If it looks and runs OK leave it. If it's a dog, take one 0.1mm shim back out and see if it's better.