The New Cross overground route is not used a lot because the service frequency isn't good enough. I occasionally go via lower sydenham to shoreditch which is very easy from FH. The obvious route would be lower Syd to New Cross, cross the line to the overground and then straight to Shoreditch but if the train is late which of course never happens i miss the connection and wait 15 mins so i have spent 20 mins on a connection. I don't bother trying any more as it is a rubbish interchange. Despite that a considerable number of people use it and I am sure TFL know that increasing the frequency would make it work as an interchange and so are waiting for the right time to do it rather than closing it down.