Hi Jim
Here is how I started getting smoother on my lines, and maybe it will help.
When I scribe my line with my wing dividers, I go back over that line with a tickler and really get a deep trench so that my swivel knife has a bit of a trench to follow. You still have to take it slow and be careful, the knife will not follow your tickler mark easily but it helped me until I got a lot of practice to where now I don't have to do that. Maybe it might help.
The other thing that I started noticing is if my blade starts getting the least bit sticky I strop it. I strop a lot more than I used to.
Anyway, I hope that helps you out a bit.
side note.... the outside border of a saddle always starts at 5/8ths from the edge. At least thats what I have been taught.
Best regards,
Keith Valley