What do you mean altitude of the launch site?
Range is primarily determined by missile ballistics. Usually that's the most neglected factor - so missiles are just given launch window... max range, max radar alt whatever, but they can't fly that long OR fly with 8-10 Machs.
You need a proper radar, set accurately - that can see, and see only as far as it is supposed to see. Range, strength, altitude settings etc etc.
IF that works as it should, then you can set the SAME data into the launchers and the missile as well.
Missiles usually have no problem with altitude, they are even too good at vertical accelerating - that's why the radar has to be limited NOT TO launch the missile to unreal heights.