Series 6 Workout Distance Not The Same Between Two Watch/Users

Not sure how many people workout, i.e. walk, run, bike, hiking outside with a partner and compared the workout distance and average pace.

The wife and I workout together, mostly walking, biking and hiking, and we originally had series 0 watches and understood it is basing distance on stride which is calibrating against the connect iphone's GPS. Our series 0 watches never displayed the same distance nor the same number of steps traveled (hers was always lower number of steps, she is shorter and you would expect more over the same distances but she gets less). However, over time the distance traveled got closer but steps were always off. Her watch showed crossing the 1 mile mark within ~100 ft of mine, as you can image this error would add up over longer distances traveled. We accepted this due to it using stride verse actually distance traveled.

We both upgraded to the Series 6, which supposed to rely on true GPS to determine distance traveled. We went through the normal workout calibration routine Apple Watch requires. We now have done outdoor activities every day for the last month. Both watches still do not show the same distance traveled and the average pace are different since distance travel is wrong. Every day we do the exact same path and her watch is consistently showing ~0.05 less miles for every mile we go. If we go 2 mile her watch is showing ~0.1 miles less (520 ft). Keep in mind we are right next to each other going the same pace at the same time. But if we do a 10 mile hike it is not always off by a 0.5 of a mile it usually off by 0.25 up to 0.5 miles at some point it seems to begin correcting itself.

Since her watch is always showing less distance traveled it translates into less of a workout due to calculating her pace as slower than mine. At this point I am not sure if my watch or her's is showing the accurate distance, I have not measured it against a calibrated mile at a school track. At this point they are  not showing the same distance. I think everyone would agree if you walk or bike a mile every Apple watch should show the same distance, it should not be up to debate (yes I know GPS signals are not accurate down to the foot, but each watch should show the same error).

To understand why this discrepancy exist and see what else is wrong, I took the total time of the workout and the distance traveled and manually calculate the average pace. The average pace is wrong on the watch. The watch is consistently showing a faster pace (2%) than what I manually calculated. The math is not complicated for average, it is just 60/(workout distance/(workout time/60)).

I am now doubting any of the measurements on the Serie 6 Watch are accurate since it cannot calculate a simple average pace.

Has anyone else seen similar things when you compare to someone else's workout. For anyone who is married and competitive, you can understand why this is an issue.