Welcome to the forum, wicked_caitiff!
From the rulebook:
@rulebook:
Scramble
Scrambling is a special movement that the defender can make at the end of this phase [i.e the attacker’s combat move phase]. It must be done after all of the attacker’s combat movements have been completed and all attacks have been declared. The attacker may not change any combat movements or attacks after the defender has scrambled.
So the attacker decides where to put his planes in his combat move phase. He hast to consider, that the defender may possibly scramble. The attacker may place his planes in the seazone where a potential scramble could occur. This is explicitly stated in the rules, too:
@rulebool:
… Moving transports and their cargo into a sea zone from which you plan to make an amphibious assault counts as a combat move,
even if there are no defending surface warships there and there is no potential for air units to be scrambled (see “Scramble”, page
15). This is also true of any units that will support the assault. Further, if enemy air units could potentially be scrambled to defend
the sea zone, additional units may be moved into the sea zone to combat them in case they are indeed scrambled.
Your planes would be the “additional units” then, that in this case may be moved into that SZ in the combat move phase, because of the potential scramble, although the SZ is not hostile at this moment.
So it is correct to differ between ait units that are moved into the SZ to meet a potential scramble and air units that move into the land territory in order to conduct combat there (so your assumption stated in b) is correct).
HTH :-)