My 5k PB on this method is in the 16:30s and I do my easy runs around 5:20/km. Though all my easy runs are done on a route with a long incline in the first half and long decline in the second half, so my heart rate is usually higher in the first half but the whole run averages out to around 67% of max heart rate. I kinda agree with 'not a flatlander', because of you lived in a really hilly area, you would have to walk half the time to get your heart rate down which would be really impractical. Maybe in that case it would be wiser to go off pace and use sirpoc's elevation calculators to determine how much to slow down. For what it's worth, before his injury Cheetodust used to do his easy runs on a really hilly route and I think he was running like 6:30/km on the uphills. So I don't know what the answer is, if you're recovering fine for workouts, whatever you're doing is probably working