In current missile, what is the guidance law used at terminal phase in homing missile guidance? In current missile, what is the guidance law used at terminal phase in homing missile guidance?

eg: Proportional navigation, Augumented PN, Optimal Guidance Law, etc

At what distance the terminal phase guidance engage for Air Interceptor Missile(AIM) { eg: sidewinder, Derby, etc }. This is for active seeker(radar). And what is the terminal phase guidance used for active (radar) seeker.

what are information get from seeker to guidance system at terminal phase using active seeker(radar), other than Line_of_Sight(LOS) and Relative range(R) between missile and target.
According to this easy to read brief introduction:

Optimal Homing Guidance Laws


  Other Optimal Homing Guidance Laws, many modern guidance laws require
  an estimate of time-to-go (tgo), which is the time it will take the
  missile to intercept the target or to arrive at the closest point of
  approach (CPA). The tgo estimate also is a critical quantity for
  missiles that carry a warhead that must detonate when the missile is
  close to the target.