The little tiny hole on the bottom of the Tello (between the visual positioning sensors) is for the barometric pressure sensor to operate properly.
I cannot find, above this^^ post, where anybody asked about what your are describing here. I expressed curiosity about a specific, and unique hole, which is very uniform, in the bottom of a Tello, and I posted a photo with a red arrow pointing at it. Can you tell me how yours is a relevant reply?
And if I pretend it is relevant , and read through to the end, I cannot follow what you are describing. The VPS is 3 round sensors in a row. Is the hole you speak of between the port side sensor, and the center sensor of the VPS? Is the hole you are talking about, that "is between the VPS sensors," between the starboard side sensor, and the center sensor? I don't even see a hole that your're talking about. To me, it sounds like your are describing the recess where the VPS camera sits, in between the IR sensors. Maybe you have new Tello revision, where they ripped out the VPS camera and put a barometric altimeter there. Even though whatever on Earth you are talking about, has nothing to do with hole I referenced at the top of the thread, Im very curious now. Can you post some photos to clear all this up?
If it helps, this isn't forum focused on holes, nor a thread with holes as the primary subject, both of which would have to be true for me to consider your reply remotely relevant. I welcome your clarifications.