You're both correct - SFO is just a lot tighter than LAX, at least in J. Seems like most days of the week are blocked out , rather than sold out.

I second the F/J combo idea - this is how we used our first 241 to YVR and it was an excellent way to use it. Yes J was a bit of a come down, but I glad we a) spent the 25k to experience F (on a day flight, ex-LHR) and b) didn't spend a further 25k on the way home, since we slept most of it.