Actually, 3 PRF modes are high, medium and interleaved.
Detection ranges against approaching fighter aircrafts at same or higher altitude;
Su-27/33 radar: @High 120km, @Interleaved 90km, @Medium 60km
MiG-29 radar: @High 78km, @Interleaved 59km, @Medium 39km
Detection ranges against receding fighter aircrafts at same or higher altitude;
Su-27/33 radar: @High 20km, @Interleaved 30km, @Medium 40km
MiG-29 radar: @High 13km, @Interleaved 20km, @Medium 26km
Ranges will be 66% of above values against targets at lower altitude.
Ranges will be 60% when you are at altitude of 800m or below.
Ranges will be doubled against larger airacrafts (cargo, awacs, tankers etc.).
Ranges will be 20% against stealth F-117.
F-15 has no PRF mode in LockOn. Its detection ranges are same as 'high' mode of Su-27/33 against approaching targets and 'medium' mode against receding targets.