BA files different YQ levels for connections as it does for point-to-point, just as it does for fares. The charge is still based on flight duration - but varies depending on your point of departure. A longhaul ex-DUB is going to have more YQ than a shorthaul ex-DUB. Same for LHR. That the LHR longhaul YQ is more than the DUB longhaul YQ, is just one of those things. Like ex-DUB fares...
(PS. I think you meant DXB for your destination?)