Fenix 8 51mm: AMOLED vs MIP - battery life.

Have both on hand. Multiple charge/discharges done. Hard reset done where everything is erased and started from scratch. Latest 11.90 installed. Tried Betas too. Tried built in as well as my own watch faces with no every second refreshes. 
AMOLED - advertised battery life with AOD on is 13 days. Watch in reality gets easily more than 15-16 days with few GPS hours. 
MIP - advertised battery life of more than 30 days. Watch in reality gets barely half of that 15-16 days.

To me that is insane. Can anyone from Garmin try to explain this logic??