Sleep experts needed!

My 6mo is going through a sleep regression, up every few hours at night and usually has a false start. Current schedule is stuck between 2/3 naps per day and sometimes we get messed up because his 3rd nap will be at/around 6pm when bedtime should be 8. Wakes at 7:15 every morning.

Question is, why does my son seem to go to sleep easier and have the longest stretch of sleep at the end of his nighttime sleep? To elaborate, he seems to go down easy after a wake up at about 3/4am and sleeps very soundly until we have to wake him up at 7:15 for daycare. I’m sure he’d sleep longer if we allowed.

I’ve always thought the first stretch should be the longest. What could be causing this?