The reCaptcha has been for a while reading not only the user’s input to the captcha to solve, but also the behavior of the user as he interacts with the website, even before the captcha is displayed at all.
In other words, the Captcha is able to tell humans and bots apart (with whatever degree of certainty) even before the captcha is displayed, even if it isn’t at all.
Also considering the insane amount of input they gather. A few false negatives are to be expected to I don’t think it really matters where you click unless you miss ALL of the squares. In fact I’d encourage you to fail them on purpose and report back your results Just be aware that from that point on the captcha may label you as a bot for future login attempts in other sites as well, so be sure to use a separate browser window and unique configuration (window dimensions, addons, etc) to be on the safe side.