I just found out that if you start your player flight one second after the others, this can determine where you start on the ramp. You have to pay attention to the parking diagram in the manual. It lets you know which order the flights are handled in the parking spot sequence. If I have a mission with 4 2-ship flights and I want to start on elevator 2, my flight's start time needs to be 1 second after the flight occupying spots 3 & 4. If I want to start on elevator 4, my flight's start time needs to be 1 second after the flights occupying spots 3-6. See attached test mission.
This post is helpful in determining which spots uses which catapult: https://forums.eagle.ru/showpost.php?p=4344957&postcount=8 SC_Ramp_Start_Test_CAUC.miz