Redeploying various AA units

[jawi]

Here is something I still haven't understood, even after consulting the manual:

When I redeploy various AA units—for example, moving them from one city to an urban combat zone (OHK) or to another city—the number of Action Points (APs) deducted varies; sometimes it's more, sometimes less, and sometimes none at all.
I just keep noticing that, all of a sudden, a large number of APs are missing.
Is there no way to send AA units from other cities to frontline cities without losing APs?

Could someone please explain the details of this?
That would be great.
Many thanks in advance.