2015 Nissan Rogue: theory on its lackluster heat

I own a 2015 Nissan Rogue model S. It’s a great car and has given me no problems except it has lackluster heat when the ambient temps are 5* or below zero. The mileage us 52,000. There are 2 thermostats in this engine. The upper one is a 180* and the lower one is 202* I’ve been battling this heat issue for as long as I’ve owned it. It’s been in the shop many times. The factory still has the warranty in place and is trying to get me some heat. If it were me fixing it I’d change the upper thermostat to a 195 or 202* My theory is the hotter engine is more efficient than one that runs like the thermostat is stuck in the open position. Factory Reps say it’s indicative of 2015 and 2016 model S Rogues. Any thoughts!