FM signal range
Might be 20cm, might be 100m. Depends on;
Shielding eg VCO inside a metal box or not.
Power level in the VCO.
Power supply decoupling.
Length and shielding of power supply and output pcb traces.
Receiver sensativity.
radiation pattern from the VCO eg if you have a solid ground plane on the bottom of the pcb it will radiate less downward.
Postion of receiver relative to VCO
Receiver antenna gain, pattern and orientation.
Local noise at the VCO frequency.