Back in the day, before I started using basecoat blender, I would apply a coat of Bulldog on the entire panelJC Clark said that Bulldog adhesion promoter will work for blender.
before putting basecoat on, mainly when spraying silvers, it fills the scratches and gives a good even surface
on the entire panel so the base lays the same all over. Even sanding the panel first with 600 will sometimes
show scratches with silvers, especially out in the blend area where the new paint is transparent.
The Bulldog eliminated that, it says it will fill 320 grit scratches.
It always worked really well for me.