I realise this comment is after the horse has bolted but when lighting these scenes a few things are crucial – eliminate spill from the green/blue screen back onto the subject. Try lighting the rim of the subject with a straw or amber gel on the lamp – Getting an even lighting situation is nice but incredibly hard and much time is wasted trying to achieve it. Finally doing a green screen outside in the sunshine is the best keying situation I’ve ever achieved, even if I am shooting the for an indoor scene.