It is not correct to say that when Heathrow is on easterlies landings are only on 9L; I see there were 330 landings on 9R during June (when there was a lot of Easterly operation). During the period from 0600 to 0700 when both runways are used for landings is the most common time to see this. BA flights are normally selected as it makes the ground taxi to T4 more straightforward.
Takeoffs from 9L are less common, and generally will occur when 9R is obstructed for some reason, either a disabled aircraft or works in hand.