Hi there, yes he's OT I think. I think you need to reduce the AM A time before that 30 min nap so he's well rested. Basically a 4 hour A time and then a short nap will make him really tired throughout the day.
We do 3 - 3.5 hours A and then a 40 min nap. After trial and error I found that 30 mins was too short for Finn and he wakes happier at 40 mins. His PM nap is then longer, up to 2 hours. It's all trial and error at this 10 month stage.
After a 30 min nap Finn can only do 2 hr 45 A at a push. So that middle A reduces a lot when they are only fueled by a 30 min nap.
The reason we cut so quickly was because we had nap refusal. Were you getting nap refusal?
Have you tried resettling at 5? Is he waking happy or upset?