There already is a buffer. In this image you’ve got about 6/7 inches from the attacker’s shoulder to the end of their sleeve, which is the furthest forward point that they’d use to draw the attacker’s line in this instance.

Why add more complexity and subjectivity into it? You’d just be creating more opportunities for mistakes. The offside law needs to be simplified, not made more complex.

They don’t use the same technology. This screenshot is from the semi-automated VAR system used by the Champions League. Not sure about La Liga, but the Premier League don’t use the semi-automated system, it’s completely manual.