My Triumph throws the first shot from a clean bore 1" high @ 100y.
I don't oil the bore until the season is over. In my experience, a clean muzzleloader is no more likely to rust than a clean smokeless centerfire.
I clean simply clean with Hoppes #9, finishing with 4 or 5 dry patches.
There are many variables that could affect point of impact of the clean/cold bore shot, isolating each of them and re-testing will be nice off season project. I'd start with eliminating the gun oil.
YMMV
Good luck on your hunt!