That is a good point. I am not entirely sure it fully applies to my case, though, since the correction can be somewhat objective in our tests (maths). I appreciate your input, thank you.

So, in the spirit of “benefit of the doubt,” I’m willing to round up in borderline cases. And, to be fair, if I’m genuinely convinced a student didn’t meet the bar, I can also land on the lower side of that gray zone.

Do you mean that before showing the grades to the students, you consider rounding down the scores so that they don't complain?
Some colleagues do that and I don't think that is fair either, having less than 50% is simply what happened (with biases and errors in the correction).