You hit it right on the head, Roger. I know chickens and dogs and cats are different but my experience has been years of working for a (very good) vet and helping in surgery. He liked to explain step by step through his surgeries no matter how many years we'd been listening. And he always stressed to get ahold of the vas deferens as far back away from the testicle as possible before severing it. I made a special point of doing that the day we had the caponizing clinic at Poco's house. I bought a cauterizer but I think the area you've got to work with is just so tiny it would be hard to get in there with it and not accidentally cauterize the intestine. However making darn sure you've got the entire testicle and making sure to cut as far back as you can from that (I believe) is the trick to avoiding slips. When you use the straight "grab and pull" technique there's just no way to control making sure you get every piece of that tiny chunk of testicle. It feels like the piece of fat in a can of pork and beans lol
I've got 3 Brahma boys I'm doing today, the 1st ones I'll be doing alone. You've made me feel better though. At least my 1st set 2 months ago was done under the watchful eyes of 2 mentors. You're beyond brave to attempt it alone the 1st time!
Small space has been my experience, too. No room for grabbers, work lighting and cautery tip, too. Some testes are just attached tighter than others, some are easy. Experimenting on cockerels that you are processing anyway, and have already killed, is next best thing to having a mentor. That still doesn't prep you for wriggling patients and pulsing arteries, tho...