Enemy-AI Collision detection[help]

Hello i hope i get help from the talented ppl here… i am developing a simple los based game like security where if i fall within the LOS of enemy i am out… well for testing i wanted the movement of the NPC’s to be intelligent rather than tween them… I implemented a simple chase algorithm and did some collision testing on the NPC …but i am unable to show any AI characteristics for the NPC and collision of the NPC sometimes gets wrong on certain edges… Any help for making the NPC more intelligent and improving the collision wud be greatly appreciated… I am attaching my file…

The blue circle is the chasing NPC and is being tested for collisions… Plz help ppl as i am sweating out to get it right…