The tray table is kept in the armrest. I was in seat 3A and the armrest on the left (towards the window) is fixed. The middle armrest is oversized and immovable. Seat 3b the tray table is in the right arm rest. There is a little room between the armrest and side of the cabin (about 4 inches or so) where you lodge pillows and blankets down.

Hope that helps.