We had M and G at Manchester in about 2008.
Can't think of the exact date, but it was the year when Biffy Clyro were the support.
We got back in to the arena in time to see about 4 Biffy Clyro songs (no great miss there then!)
We had floor tickets and got let in, as you suggested, near the back.
Still managed to get our way towards the front so it wasn't such a problem.