My engineer goby is about 16 inches I have never seen any kind of aggression towards other fish, but I did hear they can get nasty if another fish is compromising his turf ,
If it feels threatened of course he is going to defend his home , mine since day 1 always had good social reaction with all the fish in the tank , keeping him well fed should mellow him out too .
he loves the little clown I have as he brings him food , I also think that if a engineer is brought in after all the other stock they will be a lot less territorial and a lot more social,
Fish are like lifesavers
They come in different colors