...and above all, HOJ is by definition not possible with command-guided systems.
I would bet on visual channel. As I heard, ol'Karat TV camera works amazingly good at night (is even oversensitive for daylight - can get broken if directed at the sun). 13 km does not seem impossible for maintaining the guy in sight, once caught, and then - T/T, no exact range indication needed, blablabla...
RCS varying - also seems possible, and in any case helpful. F-117's "stealthness" was heavily dependant on the angle of illumination. After RWR warned the guy, he might have lost his nerves, began maneuvering agressively, and so on...
