There is no mystery here.The San Francisco 49ers should be more worried about the cornerback position than any other spot on the field. In our poll this week, we asked readers to vote on the biggest position of worry for the 49ers. Cornerback received an overwhelming 82 percent of the vote as of 8:55 a.m. ET Thursday. Backup quarterback received 10 percent, while inside linebacker and center each received just four percent of the vote.The lopsided vote is not a shock.