artist-flood-fill-right-border

artist-flood-fill-right-border is a variable defined in `artist.el'.
Its value is

window-width

Documentation:
Right edge definition, used when flood-filling.

When flood-filling, if the area is not closed off to the right, then
flood-filling will fill no more to the right than specified by this
variable. This limit is called the fill-border.

You can customize this variable.