How does altitude effect carb adjustment on 25 hp johnson

[Coastalguy]

I have a 97 25hp 2cyl 2 stroke Johnson. No boat shop/dealer has ever been
able to answer this question. I live in Denver(5200') but as most boaters who live here do I leave the sea level high speed jets in the carb and just drop 2 "
prop pitch with good results here. Some guys change jets for Mountain use.
My question is when I go to a lower elevation it seems to have very little
effect on the idle mixture setting. When I go to adjust it I usually wind up in
just about the same place if I watch the adj screw as I adjust it. I just spent
2 years in KY at or close to sea level and it seemed to make little difference in the adjustment. The same thing happened years ago with an older 15 hp Evinrude 2 stroke when I used it in Maine it required no low speed carb adjustment, when I went from here to sea level and back.
Are these 2 stroke carbs of a different design because every 4
stroke carb I have ever seen needs the idle mixture readjusted as you make
a big change in altitude?

I bet somebody knows the answer here.

Thank you coastal guy