I have switched to the 5/8" needles three weeks ago and noticed no difference. I was using 1" and getting a few knots after a long period with no particular issues. No knots with the 5/8". My doc indicated you need enough length to get past the fat in the area you are injecting (ignore SC concepts here). I am injecting into glutes only and I am also very lean in that part of my body. Not sure what I am saying is fact-based, but it is working for me, two injections per week.