As an following post of this one ( http://captainsim.org/yabb2/YaBB.pl?num=1299099692 ) & after some tests I made, I confirm that maximum distance to shoot any missile is 50 nm.
Though missile can travel for much farther distances until target (I think unlimited distance...), radar lock cannot be achieved further than 50 nm.
Now, what you should edit in CSweapons.xml for any missile to get it as far as you want, are the following 4 parameters :

              <Name>AGM-88</Name>
              <Desc>AGM-88 HARM</Desc>
              <HudString>AGM88</HudString>
              <Pix />
              <Container>CS_Weapon_AGM-88</Container>
              <FxWake>csweapon_rocket_wake2</FxWake>
              <Weight>355.0</Weight>
              <TargetWeight>50000</TargetWeight>
              <Lifetime>180.0</Lifetime>
              <CtrLifetime>180.0</CtrLifetime>
              <Efficiency>1.0</Efficiency>
              <RadiusRatio>1.0</RadiusRatio>
              <DragCoeff>0.18</DragCoeff>
              <OpArea>0.015</OpArea>
              <GravCoeff>1.0</GravCoeff>
              <InitSpeed>0</InitSpeed>
              <EngThrust>20000</EngThrust>
              <ThrustDuration>180.0</ThrustDuration>
              <TurnRate>0.2</TurnRate>
              <SteerDelay>1.0</SteerDelay>
              <SeekerAngle>3.1416</SeekerAngle>
              <SelfDestrTime>180.0</SelfDestrTime>

This way, your AGM88, is capable of flying for 3 minutes... and not just for 10 secs as per default...
And 50 NM, about 90 Km is not a short range to fire some missiles !...  ;)