Sprite Atlas UI Optimization Questions

Hi, I have some questions regarding the Sprite Atlas usage.

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1) If I have a Sprite Atlas with 10 sprites (2048x2048) but my UI asks for only one of them of 128x128. Will Unity use the Atlas or it will prefer to direct access the single Sprite file?

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2) In the case of multiple screens with shared UI sprites: Menu UI, Gameplay HUD, Level Selection UI, etc. Is it fine to have a Generic UI Element Atlas even if some of the screens only use 1 or 2 assets from the package? Or it is better to make multiples references to the same assets in specific Sprite Atlas? Example: sprt_button_1 being referenced in the Menu Atlas, Gameplay Atlas and etc.

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Thanks in advance.