Soft Coverage

I am a little confused why our corners line up 10 yards off the line of scrimage most of the time.  It seems we just concede yards underneath in pass coverage.  Also I saw Trent and Cissoko both get burned because they stared at the QB the whole time which allowed the reciever to get open.  Is there a reason for this?  I really think Cissoko will turn out to be great but I can't wait for Trent to be gone.  Brown is the defensive equivalent to Sheridan.  Why can't we takle?