I put my max HR up to 170. It certainly helped and this run was much more realistic, but it's still too low, so i'm going to take SlowLoris 's advice and put it at the max HR I experience when running - well, actually that's been 183 a couple of times, but I'll try it at 178 and see how i go, since that's the usual peak for me. I notice the adjustment has put my VO2 max up again!
Warm and muggy today, like a sauna, and i was very red in the face when I got back. but, you know what, something must be working because I had moments of total bliss on this run, just steady pace in zone 4, a sense of connection with my surroundings.