What happens if one engine fails? Automatic punchout?
From reading about it, the reason for the cold and hot nozzles on the inside side of each engine was for that possibility. It would seem that there's a tunnel between the engines which captures the rebounding jet blast when it's in VTOL, but the main reason was it could land as a normal aircraft should one engine fail, the jet blast running down the center of the aircraft.
EDIT: Looking at the 3-View it's showing just the hot nozzles are on the insides only, each engine has an inside and outside cold nozzle.