Wow, that is too much gap between your d-loop knots. I would imagine that would cause some elevation accuracy issues on occasion, the nock has too much room to move and change the angle of the arrow to the rest. I'd be surprised if the tune showed that setup to be consistent over several shots. Perhaps a bit of a tight nock fit is helping to keep that from showing.
I also have some concerns about the lower d-loop knot, it looks like the melted ball is much too small and possibly could slip through on you. Most likely when you're drawing so you end up punching yourself in the face. Perhaps it is just the picture angle but it looks sketchy in the pic.
I would recommend putting on a new d-loop and tying a lower nock set as doverpack12 recommended. I would cut the bottom portion of the d-loop from the center serving but leave the top, then nock an arrow with the nock pushed up against the top knot and tie a bottom nock set under the arrow. Leave about one serving diameter gap under the nock when tying the nock set. That will keep your nock point position where it is now. Then remove the d-loop completely and put on a new one. An arrow nock clipped to the string and slide down against the nock set will help to get your new d-loop top knot position back in the same spot. The bottom knot will just go right under the nock set.
I use bcy 3d for serving thread and BCY-24 for d-loop material. *(edited, I previously said I used .018" Powergrip for serving thread, which is true for center serving, but meant bcy 3d for nock sets, tying in a peep, etc.)
Or have a shop do it for you if you're nervous to try yourself. Having a more dependable, consistent setup is more than worth the very slight tuning you may have to do after changing it.