You could dial it up to 15 if you wanted to, but, you would need to monitor the EGT.

It's not the level of boost that is the significant parameter for determining engine damage. It's the exhaust gas temperature.

If you ran 15 psi for 30 seconds, the EGT wouldn't climb enough to do any piston damage. But, if you ran it for ten minutes, you might be in for some unwelcome surprises.

Since the spec allows up to 12 psi, I'm fairly sure you wouldn't have any problems at 11 psi.

Also, note that these are sea level specs. You could run additional boost (at the same exhaust temperatures) as you increase altitude. But, then, sea level becomes a problem without a proper EGT guage.