One thing to be aware of, which may help explain the limited range....

The path loss of a radio signal between a transmitting antenna and receiving antenna is proportional to frequency squared. At 2.4 GHz the path loss is 1100 times greater than the path loss at 72 MHz (.072 GHz). This is a whole lotl! Path loss is a result of physics and cannot be changed.

Some, but not all, of this extra loss is probably made up in the SS receiver through processing gain, and some can be made up by more efficient antennas. There is still a large deficit to overcome.

It is not by accident that our RC systems operate at 72 MHz! 72 MHz is a good compromise between antenna efficiency and path loss. Now if we could only do a spread spectrum system at 72 MHz.....!