Hand tight is good enough after the flange on the cap hits the engine block.
It will not spray or leak even if left a couple of turns loose, not recommended though just in case it vibrated loose.
The seal is on the diameter faces when the O-ring enters the bore, the O-ring will be compressed and oil pressure forces the O-ring into the upper corner of the groove where it is close to the bore.

It is not a face to face seal which would leak if it was a bit loose as the O-ring would not be compressed enough.