Huion h610 and screen ratio

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So I bought a huion h610 pro. Works fine, no problems, etc.

So I open the settings and see a "screen ratio" button to set the working area in proportion to the screen. This is where I'm getting confused.

My screen has the native resolution of 1680x1050, which is the resolution it's set to. 1680/1050=1.6, so 16:10 ratio.

The working surface of the tablet 10x6.25 inches. 16/6.25=1.6, so 16:10 ratio.

Since the numbers match, I figure using 100% of the surface is what I should do, but using the "screen surface" button results in pic related.

I feel no difference whatsoever using either ratio. I tried drawing circles, connecting dots, pressing buttons.
Google gives me nothing.

Am I getting something wrong, or is this a known issue?
I'm afraid not finding the correct answer will fuck me up in the long run.