The books said old knitting sheaths were BIG, so my first knitting sheaths were big. Then, over time I discovered that for just plain knitting I really liked smaller knitting sheaths with a different leverage between the belt holding them in place and the needle. There was a clear difference; the smaller worked much better, so why did the old time contact knitters consistently have bigger knitting sheaths? I would not say that it kept me up every night, but this has been a persistent question for me over the last couple of years.
Certainly, part of it is what I normally wear while knitting. I wear a different kind of belt and I tend to wear it higher on my hips than those old timers. My normal apron for knitting fastens in the back with a clip, so normally no apron strings to tuck a goose wing or knitting sheath into.
Then, there is how the knitting sheaths were made. Green wood would have been split with an ax and shaped with a draw knife, then finished with a small knife. The last step would have been to make the needle hole either by burning it with a red hot needle or drilling it. There was the chance that the wood could check or crack. In a large knitting sheath, this made no difference; in a small knitting sheath it would have ruined the work. In a large knitting sheath, everything could have been done by eye, while for my smaller knitting sheaths I have to measure very carefully. In short, the large knitting sheaths were much easier to make.
Then there was the question of life style. Many of the knitters had gardens, orchards, fields, and animals to look after. Knitting was done in the evening after the farm work was done. A big knitting sheath is more durable as it endures farm life, and is easier to see if it is dropped in the grass or in the bedding in the barn.
Finally, replicas of some 16th century rural goose wing designs that I recently found show exceptional versatility in function. These are much more versatile than the late Victorian goose wing designs that I had first used as templates. The older designs are not nearly as pretty, but they work better. Those old knitters knew what they were doing. The Victorians favored form over function.