That is I'm afraid a risk on A319s given there is only the one exit row and they are frankly popular with the heffalumps like me. And broadly speaking people do try to get towards the front of the aircraft, in order to get off quickly, even though it only adds 15 seconds or less per row - so 20 rows back costs you 5 minutes. Which in the context of London flight punctuality is neither here nor there.

And yes moving about 3 or 4 rows from the end may give you an empty seat (and less chance of a status/business traveller). You typically will have more locker room down there too. It's just not as popular a place to sit, but the seats are broadly the same apart from the very last row - which are usually held back anyway - where the seats don't recline and may miss a window. However during the middle of the year you should really assume your flight will be full.