Two very extreme motion captures

Hi all. I have Ring Doorbell 2, and it currently set up with a Chime Pro. My RSSI to the chime is -35 and the RSSI from the chime to the doorbell is -49 (reasonable to say the least). The current sensitivity is set to max using the manual slider, not the preset option of ‘over 30ft’. So why is it that I when I watched back two separate videos listed that the first one captured me at my gate 25ft away entering the gate (which is how I want it to work), and the second video shows the postman this morning literally 1ft from my letterbox. How is this any good? I want the 25ft capture all the time.!! Any explanation would be greatly appreciated. Thanks for taking ur time to read ??