I studied above pictures and post's. I must be using a different mind-set. Here is what I do:
I decide up front on duration and average speed for the exercise session. I never deviate from that decision for that session.
I use the HRM and cadence monitor to vary stress during the session.
Hydrate every 15 minutes.
The object is to do the best average speed at the lowest peak HR.
I do not find this boring and the time goes by fast.