When you are using A/A weapons you can see an indicator above the CI Radar Screen, indicating the elevation of radar antenna (see the image of Skyracer).
In other cases you can´t see anything informing about antenna position. On real aircraft, the pilot moves a rotating potentiometer with a detent in center position, so he knowns where the antenna is.
A trick you can use is rotate the weapon selector knob to a A/A weapon (IR-RB for example) to see the indicator, set the desired position and after that, reselect the A/G weapon you like. However, for A/G weapons the antenna is set automatically (in function of flight altitude and scan range) so normally you don’t need to change the elevation.