Effective Range: the range at which the weapon maintain the 50% probability to hit the target.
Often this lead to some confusion in comparing two weapons made and evaluated in different "mindset"
More to say, the Maverick is a missile exclusively launched by planes, with a high initial speed and higher altitude. Maybe the Kh-25ML's datas come from the Helicopter launch, from very low speed and altitude.
It's just a suggestion,