I use the zones that Strava has made for me based off my max HR (which I've tested). It's interesting to note some of the changes in what the platforms call each zone. For example strava calls them:

Z1 Endurance
Z2 Moderate
Z3 Tempo
Z4 Threshold
Z5 Anaerobic

It's sort of funny to me Garmin calls their zone 2 easy. It sort of encourages people to do workouts in the grey zone (Z3) to me.

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Madison photographer Timothy Hughes | Instagram

This is my delimna. My 3x12 ride this morning. Garmin has me at 46% Aerobix (Z3) and 28% Threshold (Z4). Strava has me at 61% tempo (Z3) and 8% threshold (Z4).

I just want to make sure I am not under doing it on the endurance and overdoing it on the structured's.

Maybe it would be helpful to know what ranges constitutes a zone 2, 3 and 4 ride according to you guys?

For starters, zones should be defined relative to threshold hr, power, or pace. Not max. Threshold being the effort level you can sustain for about an hour. There are lots of threshold tests you can do 2x20, 1x60...etc. Doesn't matter that much which one you choose. Pick one and stick with it. You can read up on all these various tests. If the combined work interval duration is more than 30 minutes use 95% of average hr. If it's less than 30 minutes, use 90% of average hr.

Longer tests are usually better estimates once you get good at pacing the effort. But, whichever test you use the effort should be steady from start to finish. If you blow up the data is pretty questionable . Consistency is more important than which protocol you choose.

Z1 easy / recovery <.68 lthr
Z2 aerobic capacity < 0.83 lthr
Z3 tempo < 0.94 lthr
Z4 threshold < 1.05 lthr
Z5 vo2max > 1.06 lthr

ST is notorious for debating minutia. So, expect lots of responses detailing why a percentage point here or there will make or break your entire training plan. The above will get you close, experience will let you refine it.

Know that hr isn't the best pacing tool. It is subject to a lot of influences. So, you will need to take into account how you feel and not blindly follow the hrm.

This is very helpful. My lthr is 163. So a long endurance activity should be done at a HR of 110-135bpm?

Yep.