The Trinity Garrison. (Total War Saga: Troy)

Dudes, that's when I saw Troy and started storming her, except for the garrison and his buffs, no advantage over the other max. That's what the garrison 20 detachments (and all elite), it's a serious difference. After all, others even with unique buildings myth.squads only 16 detachments in the garrison. The question appeared - why after the capture of Troy the number of garrison automatically reduced to 15 detachments? (the same with the heritage of Paris and Hector). The very construction of the city begins to give 5 units less. Is there any way to keep such an awesome garrison or not? (The toad suffocates, because it is pitiful to leave the army there all the time)