Hi Ekta, it sounds like you've done the right things in terms of adding A time and capping naps. You don't have to cap both naps at this age, you can let him sleep for 2hr for the first one if you'd like. The trouble with this is that some LOs will refuse the second nap if they sleep too long in the morning, so then the morning one must be capped.
Typically, long NWs are considered UT (not enough A time, as you said), but can also be down to teething/discomfort or developmental milestones (practicing crawling/standing/walking, etc). Do you have any of the others going on?
What does your EAS currently look like? I don't know that there is an ideal one, because every LO needs something different. Is he an independent sleeper during the day and at BT?
I'm guessing this might be close or work well for your DS...
Wake 7am
Nap 1 11am-1pm
Nap 2 5-5:30pm
BT 7:30/8pm