Mxsmanic wrote:
Am I correct in assuming that changes to mixture diminish with increasing
altitude? That is, a mixture change is more important and larger when going
from sea level to 5000 feet than when going from 10000 to 15000 feet?

Nope. As a matter of fact, my old engine that had the altitude
adjusting carb had the it's automatic adjustment give up around
10,000 (by definition) and you then had to lean manually.