That might prevent about 1% of away fans (ironically, the 'true' fans who support their local club) but the other 99% with Sussex / Surrey / London postcodes will be unaffected.There needs to be a postcode ban to begin with, anyone that lives in close proximity to the away team with no purchase history with other clubs should be banned, seen other clubs do this.
Edit: Had two away fans in front of me in ESU - they were quiet, well-behaved, caused me (nor anyone else, as far as I could tell) any problems. I did chuckle that they missed our first goal(still on the concourse). and left swiftly after our 3rd