In my opinion a banner is supposed to be read by it's audience (in this case the fans inside the amex) so a 1.8m high banner will only be read by 50% of the target audience.
I don't know the limitations of the area but if it's possible the height should be at least 3m to have any affect in a large stadium and "sussex by the sea" would only be seen by about 10%. I voted for no.1
Are you a moleman? This will be bigger than most of the advertising boards around the ground, will it not? I cannot imagine those being more than 1m tall, and I can read them all from my seat very clearly.