My gaming group in a few encounters will be hitting level 14. I plan on taking the arcane familiar feat, and choosing the bat familiar.  My plan is to have the bat passive inside my cloak to gain the benefits of its blindsight while scouting around for my party.  Assuming I myself am hidden, would I still need to roll for the bat using my modifiers? And would I have to have the bat on my shoulder for its blindsight to even work?