Hi @alexandre. For the purposes of accessibility communication, in fact the button sizes on the screen will be a more important factor than any marginal change in eye tracker accuracy relating to screen size when it comes to reducing false positives.
In addition, it is generally true (up to a limit) that a larger screen should be easier to calibrate with.
The EyeX (And Tobii products in general) are designed in such a way that screen size is not a major influence in accuracy, except of course at the extreme scales of dimension.