I’ve noticed that with new fish you have to really get them used to your presence. As young fish, any sudden movements will send them instantly into cover. When I’m approaching my tank I’d be sure to let them see me from a couple feet away, if they haven’t then approach them slowly. That’s what I’ve done with all my cichlids and most recently my young male Labiatus, within 2-3 days he’s now front and center at the tank when he sees me. Of course every fish is different and Dovii from what I’ve heard can be quite skittish. A 12 inch Dovii is still pretty much a young male, I guess equivalent to our teenage years.
Does he eat in front of you? If he does then he associates you with food which is already a step in the right direction. I would say dithers but the Dovii being a massive piscivore will probably pick them off, so the only options I think would be to give him time or add more hiding places for him.