My own experience has not been as sucesful. In fact I have yet to win at Aerolotto ex LHR or ex YOW-LHR or ex YYZ-LHR.
This year I thought I was smart to book a mid week flight to increase my chances. This was in May. No luck. Same thing on the retunr flight 3 weeks later.
The year before that I tried to upgrade at the window (I am E) in Feb. leaving on a Friday and returning on a Monday- no luck again.
I think U fare is too much to guarantee sucess at upgrade, so I will buy L or other low fares and keep trying with SSWU. That is why I will miss having B and H available for upgrade .