I recently purchased the SS Buckle Prong. My dog is between two link sizes. What should be done about in-between sizes?

I recently purchased the SS Buckle Prong w/ DD collar from your website. Before I ordered, I measured Sadie (a 15 month old Doberman) using instructions from your ebook on proper fit/position for a prong collar. Her neck measured 14 inches. I knew I would have to remove several links to get the correct fit since the collar measures 17 inches. I wanted the buckle collar because I have trouble with arthritis in my thumbs, so pinching the links to attach the collar is sometimes painful.

I received the collars today, removed three links which seemed to be a good fit, and we went for a walk. She is fairly well-behaved (she's a rescue dog), but does occasionally pull away from me when she sees a squirrel. Today she pulled only once. The collar worked beautifully; however, during the course of the walk, the collar slipped down somewhat, reaching the position your website shows as too low. When we got back home, I removed one more link (now a total of four), but when I fastened the collar this time in the proper position, she choked, and the prongs seemed already to be pinching.

What should be done about in-between sizes? Perhaps she will gain more weight, and the collar will fit better when she does. In the meantime, will any injury or bad habits occur if the collar is lower? I am using the dominant collar as backup, so even if the looser prong collar gives way, she will still be under my control.

I have enjoyed reading your ebooks and perusing your website. My last obedience training experience was thirty years ago with another female Dobbie (as intelligent as Sadie is and when I was younger and more nimble) using William Koehler's methods. I have found the addition of treats to be effective, even if Koehler may be turning in his grave.
Thank you in advance for any advice you can give.

Louise