The best way to check the range of your FPV system is in the air, preferably with a spotter to avoid losing your RC model. Ground range check will give you very short ranges when compared to aerial.
Keep the antennas for the receiver/transmitter in the upright position for optimized performance. - Install the transmitter as far as you can from any other electronics i.e. ESC, motor even camera. - For best reception, the receiver's antenna must be placed under open sky, with no obstructions such as roof, building, under trees, inside of trailer or car etc.