Thank you. Excellent thoughts on this. I did not realize OH pressing works traps, but now that I actually stop to think about it, they are working to keep your shoulders and arms moving up and in as you press and when your arms are straight overhead, your traps are totally tight.
I had always thought of pressing as a "push" exercise, whereas all the shrugs, rows, deadlifting, etc as "pull" exercises. So I always did them on back days before, but as someone pointed out, that's a lot of sets, so I was always trying to juggle shrugs among other things to balance my daily sets, hence the initial question. Now, I'm realizing if I OH pressed one day, then did Shrugs the next, it was probably counterproductive.
Still, I also can't get past the simplicity of "they're on your back, so do them on back days" as Trevor pointed out so eloquently.
Very interesting anyway, thanks.