Added 3 minutes ago
You can find more information about how the creature type affects its position in the recruitment window and its dependence on buildings in the quote in my first post in this thread. All the information I was able to find through trial and error is organized there.
Added 5 minutes ago
Ah, I understand. If you used the Archangel as a base, then it should be read as an upgraded creature. However, it is very possible that the game determines whether a creature is upgraded or not based on the "base creature" line and all values set to "unknown," and it records it as an unupgraded creature. That's why it places your angel in the first slot in the recruitment window because it considers it not to be an upgraded unit.
Try setting your new angel's base creature to the Archangel or even someone completely different, like a peasant. It might help. After all, it worked for me with the Gremlins. They appeared in the 2nd and 3rd slots in the recruitment window, so it must be possible.
Added 8 minutes ago
There is also a tricky line in the creature's xdb file called "pair creature" or something similar. In theory, it affects which creature can appear as an additional unit when fighting this creature or a neutral creature. But who knows? Maybe in this case, this line also affects something. Although that is unlikely.