Need an advice, how can have better chance to found more rare/elite npcs. Sems increasing my sensors isn't work, cus i constantly have 0 rare npc on my battle tab when i had +1000 or +2000 sensor power.

depends ...... what's your rank ? how many npc's have you tried to kill ? you can't wait for them to randomly appear when your battle tab refreshes......you have to slog through a couple dozen commons to find any that are good

NPCs spawn randomly. As long as your scan is more than the cloak value of an NPC, it is possible for it to show up for you. Keep in mind, that Rare means exactly that. You basically need to churn your way through bunches and bunches of NPCs to dig up Rares and Extremely Rares. Having 2000 scan instead of 100 scan does not give any boost to the rate of Rares.