Maybe this brings the case for barriers at these stations? Then again that would mean that a large amount of stations on the whole network should get barriers.
I'd imagine G4S staff would be present at those stations on some days. They aren't always at the station you'd expect which is probably the best way of catching fare evaders - one day on the Chester-Manchester via Altrincham line, Greenbank had RPI staff present but larger stations like Altrincham, Knutsford and Northwich did not.