Mailbox sensor location on back of mailbox?

I am so not tech savvy, so please forgive me if I didn’t post this correctly. I have a new mailbox, and just purchased a Ring mailbox sensor (and bridge). I think I have it all set up correctly, but now I need to attach the device to the mailbox. I really don’t want to put the big and bulky sensor on the door and have seen a couple videos where some users have added it to the back of the mail box. Is this Ok? I think the motion of opening the door will move the mailbox so can that be enough to send and alert? Any advice/I formation, greatly appreciated.