How MOD-RFID1356MIFARE read through metal? Any options?

[JohnQPublic]

I have the HMOD-RFID1356MIFARE
https://www.olimex.com/Products/Modules/RFID/MOD-RFID1356MIFARE/

I works fine. Now I need to get signal through thin-sheet metal? I plan to put it in a mail-box -like enclosure. The RDID reader appears to have holes in the board that would enable to extend the copper wiring. How about if I connect the copper to the metal in the mailbox?