I had a Ornate that was mean to any bichir that I put in with it. It would just chase them around and bite them and it did not care about the size. Some of them just turn out to be really aggressive.
Keep us updated on the situation. I was going to suggest adding more Polys to see how it goes. Another thing is, if you have a spare tank, remove the Ornate for a week or so and then put him back. This may give the impression that the Delhezi has control of the territory and it might be a little more submissive towards the Del.
My female ornate when through an aggressive stage when she hit about 6". Lasted until about 12". Generally it was directed at other ornates only. She is now with two other ornates with no issues.
Mine is cb I believe it is a she? But it has calmed down a bit the lap kicked it out of its hiding place and the endli got into a scuffle with it already. So as of now it is a little nicer, it must have needed a someone to put it in its place. But its too soon to tell.