Bike HR training -- personal case study

So I have read a lot about HR training in tri-talk, and followed the guidance of Shelly123 and dck4shrt when it came to building base on the bike. They would yell at me for going to hard thx guys

The Background:

The first ride I ever did with a HRM was a loop around BWI airport; I rode at what I felt was a comfortable pace. The next day I did an LT test on the bike, and have tried to log every ride since with extended HR info in BT. This first ride was on Dec 19, today I did the same ride in same direction on the loop, starting at almost the exact same spot (I parked .02miles from the first spot, hence the ride is longer by 0.04).

The Variables:

Bike Positioning. I had a professional fit which made my aero position slightly more aggressive during the last 3 months, dropped the handbars 2 spacers and moved the seat forward 2cm to account for the shift. Also replaced SPD's with Look pedals... beyond that almost everything else remained consistent on the bike.. and physically I am approximately the same weight. I did ride 25 miles yesterday with approximately 2600ft of climbing, so I had some fatigue in my legs today, but it was not bad.

Weather

Date                 Temp     DewPt        Pressure     Wind
12 PM  Dec 19   38         21.0           30.13          S 8

 Date                 Temp     DewPt        Pressure     Wind
5 PM  March 3    62.1      37.0           30.03          SE 9

Today was warmer, and the wind was very similar. It is a loop so you will get hit with headwinds, tailwinds and crosswinds

Training:

Since Dec 21 (The day after LT test), I have ridden approximately 820 miles in approximately 50hrs 30 min. I did not really do any hard interval training, I did do some hilly rides, but in general I mostly tried to keep the HR in Z1 and Z2 as reflected by the overall large amount of time spent in the two zones. Time in Zone is as follows:

 The Rides:

Dec 19: Distance: 12.08 Miles, Time: 45:10, Average Speed: 16mph

HR Avg 163 Max 183

Z1 4:55
Z2 12:20
Z3 11:21
Z4 12:51

March 3: Distance: 12.12 Miles, Time: 41:12, Average Speed: 17.6mph

HR Avg 155 Max 169

Z1 8:21
Z2 20:06
Z3 8:36

Conclusion:

So for me it shows that my training in Z1 and Z2 has lowered my average HR by 8bpm (Z2 vs Z3), lowered my max to Z3 instead of Z5 (for this ride), and increase my average speed 1.6mph on the same course with the much lower HR. I was also careful today to back off if I saw the HR climbing, and keep it in Z2 as much as possible.  I personally was blown away to see the HR/speed differences.