I think you are on the right track.

I started riding / training with heart rate when I restarted cycling in May 2006 @ age 57. I found it confusing and that my heart rate tended to be high most of the time. Also, it was easy to get to a high heart rate or maximum. Over time, I received guidance from cycling coaches, read books / articles and gained a lot of experience just riding and especially racing.

Here are some of my experiences:

1. When i first started out, my body was not efficient at channeling blood to power producing muscles and temperature control under higher power so my heart would pump faster and flood everything with blood. My face used to get very red especially if it was hot. That does not happen any longer.

2. My heart rate would go high and when I would stop or coast stay high. The rate of decline was slow. If I reduced my level of effort but increased cadence my HR would shoot up. Today, my HR drops quickly the moment I reduce effort @ 25 beats per minute and if I am pedaling hard at say 90 rpm and go from the front of the pack to the interior and increase cadence to 100 to 110 my heart rate still drops fast and I get a faster recovery. This is key to the ability to race in a pack or paceline. The faster the heart rate drops after sustained efforts the better the fitness of the athlete.

3. As I became more fit, it was increasingly more difficult to get to a max. Today, I need to be warmed up, a lot of adrenaline and competition in a race situation to get to a max. I cannot do it on my own no matter how hard I kill and I am really good at this.

4. The best way for me to get heart rate zones is to base them on lactate threshold. The best way for me to get that number is from a time trial. I found Joe Friel's .95 for the average HR of a time trial race to be the most reliable. For heart rate zone calculation I use the Coggan formula developed by Andy Coggan and published in his book Training and Racing with a Power Meter and plug in the number from a time trial.

5. If I lower my cadence by 10% or do low cadence climbing intervals 50 rpm, my heart rate is much lower for a large level of effort. Conversely, if I do high 100 cadence z4 climbing intervals, my heart rate is very high and approaches what would be z5 or z6.

6. Most of my training is targeted to z3 which is the 140 ish heart rate. However, the cyclist's heart as it becomes more fit gets larger and the wall thickens. It can produce a greater stroke volume per beat. So the effect is 1 beat equals a lot more power than it was before and all the blood get channeled to power production i.e. lungs, transport and muscles required for power. Other bodily functions are systematically managed to give priority to those muscles. Hence, I have to keep going faster and faster to maintain z3.

I started training with a power meter last August and got a new coach who understands how to coach with power. It was very revealing and much harder. My heart rate is all over the place from day to day and varies greatly due to rest, hydration, stress, sleep, food, digestion and etc. I read and studied Racing and Training with a Power Meter by Coggan and Allen and belong to the google Wattage group where Allen and Coggan post and answer questions.

The key advantage of power meter training is having perfect communication with my coach and doing the higher intensity intervals to completion at the prescribed power level. Heart rate is a terrible indicator for doing z5 and z6 intervals. IMO, one is better off relying on perceived effort than heart rate.

Maintaining z3 power at 100 cadence is tough. Maintaining z3 heart rate at 100 cadence is pretty easy. The reason is the rest that one gets but is not really aware of it. When I ride at z3 power, it feels relentless. On the slight downhill, the power immediately starts to drop and I have to shift into a bigger gear and work hard. With HR, I unintentionally tended to let up on the slight downhill and even a little rest for a few seconds and I am getting a recovery. With z3 power, there is not even a moment of recovery. So one learns to keep the power on the pedal and what it feels like. That is the most important aspect of interval training is to keep the power on for the duration. That is what increases power and endurance over the interval and produces the most physiological changes.

Training is not about heart rate but shocking your body. I am always doing things that are difficult. - High cadence, high power, Low cadence, high power, Low power very high cadence or high power self selected cadence long duration.

Now for riders returning to cycling to get the most from heart rate is just ride and keep it easy and observe how you react. HR is going to fluctuate but the key is you have to develop some bike fitness before you can get into more advanced stuff.

So my advice is ride a lot, spin easier gears and bias the rides to longer distances (more endurance) for a few months. Track your heart rate and over time you will learn your lactate threshold and get a better handle on the zones and how to use heart rate training as a tool.