Contact issue with OS

Hi guys, 

I've encountered the following problem with Optistruct. 

I've defined a Freeze contact (the slave is a SETGRID, the master a SETELEM[shell elements]) with a search distance equal to 8. Nevertheless, when I import the *contgap.fem file, I see some gap elements longer than 8 (specifically 14-15 mm). The thickness of the shell (master) is just 1 mm, so the problem doesn't lie in the fact that also the shell thickness is taken into account.

Anyone who has encountered the same problem?

I hope I was clear enough.

Thank you in advance