Norm, I don’t know a thing about you, but, I’ll take a shot. I’m guessing you are in your 40’s, haven’t been exercising regularly for long, and would be in favor of losing a few pounds. (If I missed the mark, I apologize.)
If all of that is correct: Then, even if it doesn’t make common sense to you, stay with your aerobic level plan. Believe it, or not, you will begin to see real improvements in a little while. How long that will take depends upon your physiological makeup, how regular you are with your training, and whether or not you are eating “better” than you used to. You have to be patient, be dedicated to doing the workouts, drink enough (I don’t mean beer:)), and eat right.
However, HR’s are just a guess at your Lactate threshold. Do you know your resting HR in the am when not awakened by an alarm? Have you (with a doctor’s permission…a cya statement) seen what your max HR is? There is always the slim possibility that you are one of the people that have a higher HR range than normal, especially if you don’t fit into the description in my first paragraph. If so, your HR range estimate could be incorrect. Like I said, it’s not likely the case.
Don’t worry about the walking part. Everybody I know does this when starting out. Most people continue to have to walk at times when they’re doing base training phasework, if they are being very strict about it.
It is also normal to say that only on bike rides will your HR stay down this low. Guess what? That’s one of the reasons riding bikes is a great way to get LONG times of training upon, at least compared to run-walking. You can keep your cardiovascular system in this Aerobic Zone, training it to be more efficient, for long periods of time with less boredom, less chance of injury, and with a convenient way to haul water with you (in water bottles mounted on your bike). Plus, ever notice how bike riders are able to smile at passersby, but runners almost never do?
Be patient, the gains will come!