Unfortunatly I do not have much advice to offer here. Hpefully evolved can chime in or you can message him, he is kind of our wrasse guru here. I want to assume but you know what they say about that. Do you have a deep enough sandbed for them to sleep in? Tangs and drwaf angels can be very territorial it is often hard to add a new fish with them established but it seems like your tank would be plenty large enough. A few weeks is not very long either. During thsoe weeks did he appear normal, eat normal, swim about during the day normally, etc?? Whenever I get a new fish I am always stressed the first few months. I feel like if I make it the first month without signs of disease or any issues than it will be a smooth ride. Its not until 6 months or so though that I feel like I am in the clear and the fish is going to be a fine lifelong resident in the reef. That is just my personal opinion though from experience, whenever I have a loss its usually in the first month.