It sounds odd, but the study linked below proves that in general, people really do appreciate delta feedback. They see it as a way to improve their performance and to be more successful. The problem is that people hate giving delta feedback.
Please take a few minutes and read this blog/study. I hope that it gives you the courage to take a chance and give someone the opportunity to improve their performance via delta feedback.
Lead the Interstates Way by giving plus AND delta feedback.