Anakin made a valid point when he said he would need to see the bike from anywhere within the stall. Harry nodded in response to his question, "Of course. I'll just extend the charms to cover the entirety of the stall." Why Harry hadn't thought of that in the first place, he wasn't exactly sure. But after a few minutes, Harry had the charms extended to the entirety of the stall. He then replaced the age line, making the line correspond with the walls of the stalls.
"The age line is along the walls of the stall as well, in case your younger self manages to find a way within the stall from a different location other than the entrance. And he won't be able to see the bike from outside of the stall. Unless he gets someone to reverse the magic, he won't be able to get in the stall at all."