It's not making the body bigger, it's making the body
unnaturally bigger. And we have to take into account what the player is doing and where the arm would naturally be
in that context. I think historical guidance is helpful here. The concept of biggering (my word for it) came from trying to identify well disguised deliberate acts--the player who deliberately puts the arm away from the body to take away the passing lane so that it will "inadvertently" be hit by the ball and not be an offense.
And as
@one already noted, the attacker handball has been narrowed again so that it applies solely to an accidental handball by the person who scores.
While the constant tinkering drives me nuts, I think this iteration of handling is far better that what we got in the revisions the last two years. We're largely back to where we were before, with biggering moved from a referee training concept to being express in Law 12, plus not letting accidental handlers score (which was kind of happening already, as the threshold for referees finding those types of handling to be deliberate was really low).