I have installed 2 mailbox sensors on 2 different mailboxes at 2 different locations. I experienced poor connectivity between the bridge and the mailbox sensor. The connection was almost always poor and it was not uncommon to have the connection drop from time to time. I installed the mailbox sensor and antenna exactly as the instructions had indicated. I moved the bridge around to try and increase the signal. Nothing worked well. So, I drilled a hole through the back of the brick mailbox and mounted the external antenna on the back of the mailbox. The antenna now faces the house. I mounted the mailbox sensor onto the inside of the back of the mailbox so that it faces the inside of the mailbox door and connected to the antenna wire that I ran through the hole I drilled into the back of the mailbox. My signal when from poor to good.
I had to purchase a 1/2 inch masonry drill bit and drilled between the mortar. It took about 15-20 mins to drill the hole.
I believe the antenna aimed directly at the house, where the bridge is located, makes all of the difference in the world.
Just thought I would share my experience with others since I could not find any help or information on my particular issue with brick mailboxes.