My Instinct 2 Solar battery life does not make sense

I'm confused about the battery life on my new Instinct 2 Solar. The specs say it will get potentially unlimited life with solar charging in smartwatch mode. After fully charging the watch to 100%, it shows I have 23 days left. From what I have seen though, the standard Instinct 2 gets 28 days in smartwatch mode. So why am I seeing just 23 days when fully charged with my solar? I have confirmed that pulse OX is on manual and the readings are with no GPS workouts.

Additionally, I'm losing about 8% to 9% battery life per day. At that rate, this device will only last 11 to 12 days assuming there is no solar boost in charging. What am I missing or not understanding?