Johnny the key is more miles. The more you do at a low HR, the lower and more stable your HR will become. If I'm unfit, I have to stop to let the HR fall, and then run at a slower pace than I had been. When fit, a small decrease in pace is enough to get back in the right zone.
Bad news here - it's pneumonia, so I've cancelled Frankfurt
RHR is a bit elevated, but I don't check it regularly anyway. "Easy" HR was up 20 beats when I last ran, on Thursday. I think the temperature has gone now. I'm going back to the Docs tomorrow...need to make my mind up soon (although I can't cancel the hotel anyway).