SetReplacements, when does it 'count'?

[Astrella]

I've been playing through the Campaigns again and looking at the maps after finishing missions to understand their workings.

I understand SetReplacements() in an AI script determines how often the AI will replace pre-placed units, trigger created units and guard posts when they are killed. I do wonder how it interacts with units being assigned to attack groups and such; cause I have noticed that the AI will freely pick units from preplaced units to add them to an attack group as well; I imagine once they're assigned to an attack group they will no longer count as a killed unit for SetReplacements()?

In any case the AI seems to replace preplaced units more than I'd expect based on testing. (e.g. SetReplacements() is 2 for the difficulty I'm playing at but a preplaced unit will be replaced 3-4 times.)

 

[Chaosium]

If you look at what they do, they can pick preplaced units to form an attack group but will train a new one to send where the unit was placed, and yes the unit sent in the attack will not be replaced, but the original position will still be reinforced