it has to be short and constant

+1. Just as we have it in Search and OGM

I don't see really what the header gives you

IMO it increases chances that people will adhere to the license when e.g. copying code from the project and adding it to their own code base. Sure, they can look it up in the file in the root directory, but the short header in the files is just more apparent.

Look at Infinispan, no noise, just code.

Dunno, didn't occur as problem to me so far. It's collapsed in the IDE anyways, so I never felt like I'm distracted by it. Maintaining the license year was a PITA, but that's gone with the shortened and constant version.