I am very doubtful that a third aircraft will be based at LGW. There are no other flights for it to operate. Looking at EI's schedule, the DUB route will be operated soley on a DUB based aircraft.
EI stated that they would reduce
capacity at LGW from 5 to 3 aircraft. The capacity of 3 aircraft can be provided even if one aircraft is based in DUB and operating in and out of LGW all day. They didn't say that 3 aircraft would actually be based in LGW.