I just flew AC100 YVR-YYZ @ 1400, on a 77W on Friday and back YYZ-YVR yesterday on Ac161 on 763 @ 1600.
100 was R5 at the 7 day window, and 161 was R3. Got my confirmed upgrade at the window for both.
However I noticed R space got zeroed at T-6 for both. AC161 had quite a few elites get gate upgraded though.
I was on a flight pass so I basically waited until my window to book so I could get a confirmed upgrade, using EF to keep track of R space.