?You're right. That would not be a 40/20, because the wording of the rules states that it must cross the touch line in the 20 metre zone. Merely passing over the plane of the 20 metre line is not enough in this case.
not to parse words...but for it to "cross the touch line" doesnt address whether it needs to touch the ground. crossing simply means going across it, be it in the air or ground.
by your logic... (and this is a wild hypothetical) if the ball is kicked long distance, bounces 25 metres out then goes over on the full 18 metres...its not a 40/20?? lol dont you see where that line of logic falls apart?
in that scenario the linesmen come running along and raise their flag at the 18m mark and the commentators talk about what an amazing kick it is they dont go back to see where it bounced first