FlaRakRad Radar Lock-on-Frame under horizon line when target object flying at low altitude

Hi, that’s my first post. Problem: When I lock the Target Tracking Radar on a target flying at low altitude, the square Lock-on–Frame is’nt shown exactly on the targets position. On the screen it follows the target some centimeters below, typically under the horizon line, aiming into earthground. By covering the frame with the round target display and launching an AA–Rocket it will explode on ground.