Naresh, I still don't know much about how you play. Are you relying mostly on national troops? Are you getting a good gem income? What spells or items do you use to decide what to research? Do you build forts? Have you ever used a supercombatant (SC)? Do you recruit at least one mage per turn? What scales do you use? What is the Pretender design you have been using recently?
Go to the
Illwinter Maps website and download the Talis map. Pick an opponent (Abysia, Ulm, Man, and Jotunheim are all fine), pick your own nation, and stick with that setup until you win a few games.
As for PD, I would recommend 11 in every province, when you can afford it. The AI knows how large your total army is. PD counts toward your total army size. Having a relatively large army can deter the AI from starting an early war with you. PD 11 also has a chance of discovering stealthy units.