Mike, I've heard that from other shooters, saying accuracy improved. I am not sure why that would be- or how it could happen. Technically speaking, the closer the crown is to a perfectly sharp muzzle face, the more accurate it will be. If coned barrels were more accurate, the bench-rest shooters would all have coned muzzles. They don't. They have perfectly sharp 90 degree, or more recently 11 degree perfectly SHARP crowns for perfect delivery of the bullet. WE can't crown that way due to having to load at the muzzle, the ball and patch having to swage into the rifling as we load, without cutting the patch, but the closest we can come to that sharp crown and still load a combination that seals, the better.
The shape of a cone is not even remotely close to a sharp crown as the cone extends down into the bore- tapered all the way - I just can't see it working to aide in accuracy. I have watched LB trying to load a .400" ball in his .40, & with a thin .016" patch(as I measured them) and it was most difficult for him, yet I load that ball in a .002" smaller bore with up to a .0215" patch using the gun's 3/8" hickory rod.
The angle for proper swaging together of a ball and patch are not a long gradual cone which extends the friction surface into a longer one, but a radiused short chamfer as used in bullet drawing dies that all bullet and case manufacturers use. The shape of the crowns on my guns quite closely emulate this and the ease of seating a bullet in the muzzle shows it works.
However - if coning works for you, that's what's important, and is what you should use.