It looks like this is evolving (for the worse right now), and more route-dependent.
For LAX-DFW (and others, competitive)
Within 3 days ND -> 9 days ND (20k)
Within 14 -> 17 days NL (17.5k)
Over 14 -> 17 days N (12.5k)
For IND-BOS (nonstop, non-competitive)
Within 7 days NS (25k)
Within 14 days ND (20k)
Within 21 days NL (17.5k)
21 days + N (12.5k)