Agreed, it's all akin to goal line technology. All the ball must cross all the line. So same with the corners like you noted, and same with throws. If a players whole boot is across the whole of the line, then foul throw.
Or holding onto it for more than 6 seconds. I counted one at Oakwell a couple of seasons ago, where the opposition keeper held onto the ball, in injury time, for 22 seconds.