Neck Knive CARRY is a very old concept. And when metal was still a rare and precious commodity, ALL knives were smaller because of simple material cost and design limits of copper and bronze.

The size of a neck knife is only limited by the constraints of individual physique. Obviously some wrastler on the TEE VEE with a bull kneck could carry a larger knife.

So, when you look at a dedicated kneck knife, ignore any gimmicks or exaggerated reduction in dimension.All survival parameters still apply, only reduced somewhat in size.

I also take exception with the materials used as hangers. We tout paracord for it's tensile strength and utility. Well, I don't want a 5MM 550 lb piece of nylon garrroting me in an accident. I also want my knife to drop IN FRONT of me should it fall, not fly off 270 odd degrees elsewhere.
My solution, and it has added utility, is LAMPWICKING, that stuff used in -oil lamps and for the best traditional snowshoe binding around. It is flat and comforatable. You can stitch a few breakaway threads and WEAR the stitch behind you. Should you get hung up it will break free and the knife fall forward, or just down your jacket, anorak, poncho. ALWAYS keep at least a shirt collar or hood between you and the lanyard even if the knife is slipped inside.
The second happy benefit is a ready source of TINDER (see oil lamp use.)

My neck knife, and there are some nice ones shown here, is the traditional puukko. I like it as much for the very ergonomic and cold weather friendly handle and deep sheath.