welcome to Chronocentric / OnTheDash, and congratulations on the Autavia.
A watchmaker could provide the technical details regarding the differences between Cal 11 and Cal 12, but as a collector I can give you some information.
Heuer used the Cal 11 in the earlier automatics (Autavia, Monaco and Carrera). There were mechanical / design problems, so the movement was modified, and was then called the "Cal 12". This Cal 12 was used in later production of the Autavia, Monaco and Carrera, as well as the later models (Daytona, Jarama, Silverstone, etc.)
As owners had problems with the Cal 11's, and sent them back to Heuer for service, Heuer updated / modified these Cal 11's to Cal 12 specifications. So most of the Cal 11's that are in the Heuers today have been modified to Cal 12 standards.
I hope that this helps.
So was your Autavia an IDF-issued Heuer?
Jeff