How to stop getting kicked off AP when at -75db?

I have a single U7-lite AP upstairs, as a temporary setup until I can add one downstairs. It's connected to a UCG-Fiber.

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It works great, except when I hit -75db signal (according to wifiman app on my phone), I get dropped. My phone will still show its connected, and shows 2 bars on the wifi icon, but connectivity will basically stop, web pages will hang, etc.

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Is this just a fact that after -75db the connection simply cannot be maintained, or is this a setting I can adjust to keep working down to -80db or whatever?

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I found a setting in the wifi options, but when I tried to adjust it it said something like setting could not be saved.

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