I've found (and booked) so many PZ or IN flights so far this year:
DEN-LHR
LHR-SFO
LAX-LHR for July 4th weekend
SFO-LHR
ORD-LHR (peak xmas travel)

If you can base your travel for Europe out of LHR you are almost guaranteed a J seat at PZ levels. Suggest to book EU short-hauls from LHR. Flying into smaller and popular EU destinations in summer will be hard for PZ/upgrade clearing, even as 1K. I also always buy premium plus fares and then request pluspoints if PZ is not available and it will go to an airport waitlist.