User blog comment:DiegoAnime3000/A lot headcanons were confirmed today/@comment-10380701-20140829010025/@comment-24177652-20140829011859

I think it also depends on the size of the object. Since it was several tiny cans, which keep in mind are very thin, making it easy for her to move with her semblance. Plus, she was right by them all. Now take Jaunes sheild. She was farther away, and it was bigger, and had a lot more metal in it. Making it harder for her to move, so she needed more concintration.