Could this be as simple as a sort of loose sprue plate fit? I've had "long" sprue cuts, and it traced back to the plate being a little looser than it should be....
High temp header paint will not work it burns easily. If you ever had headers you know this. But stove pipe paint I have had stick to headers and not burn off for years, it just turned grey. If I was to try it it would be this.
I tried it. It works and stays on. I cleaned the mold first with rubbing alcohol. Used a q tip to paint just the nose. Resizes the nose about .0035. so far just one painted mold.