POE2 Private League to Trade League Migration - Which Atlas Map is Kept?

Hello,

I've been playing both trade league Rise of the Abyssal, as well as a private league guild-self-found thing with some friends. I am finished with my goals in the private league and would like to "Migrate All" my private league character back to Trade League, so that I can move the entire contents of my stash over, along with the character.

However, based on the wording in the migration UI, I am worried that my private-league atlas map (which is not very progressed), will overwrite my much-further-progressed atlas map on my Trade League characters. Is there a way to control this? Does the game pick whichever atlas map is further "progressed" and, if so, how is that progression measured in POE2. I know that the Atlas passive TREE is merged together such that any unlocked passive points are preserved (at least, that is what I've read, but please correct me if that is incorrect), but I can't find any confirmation on what happens to the map. I believe in POE1 it just merges atlas map progression together, which is fine in POE1, but since the atlas in POE2 is a bespoke map, I'm not sure how that works.

I do NOT want my trade-league atlas map overwritten.

I believe an alternative would be to not "Migrate All" and just migrate individual characters with their inventories filled with the items I want migrated over, but I would probably have to create and migrate like 10 characters to transfer all the stuff in my stash that I want moved over, which I'd prefer to not have to do.

Is anyone able to shed some light on this?

Thanks in advance!