I don't like to go one ST against a four at back as the ST gets double marked by the 2 DCs. U can put the AMC, but don't compensate on ST, play ML MR an only 1 MC instead of two and so put in an AMC instead of the other MC. Therefore, u can play 3N-1-3W-1-2. Its a good idea to play AMC as he will keep the opponent DMC busy, thus not letting the DMC contribute in the defence behind.