If you're using the 8 inch rod then you should be getting sufficient tension. I'm no expert so I don't know if I'm qualified to help. I'll try though. I'm about a C3 and use a 6 inch rod. I get plenty of tension. If your skin is applied evenly to the bell, I don't understand how you aren't getting enough tension. I suggest you contact Chuck at the DTR website. The DTR isn't a beginner device for a tight cut theoretically, but I've seen guys do it in pictures. It can be done. A C3 is loose enough for me to use it??? My mind is buffering........ ya, you can send a pic if you want. I can tell you what I think but Chuck is an expert on this like I said.