The current loop area on a PCB which will cause problems with regard to legislative emission requirements.
The E field strength limit at 3 m distance in Standards is 40 dBuVm-1 or 100 uVm-1.
Considering OATS measurement with +6 dB in-phase reflection from ground plane, the max loop area that will not exceed specified level can be determined from:
E is radiation limit in microvolts per metre
r is distance to measurement in metres
f is frequency in MHz
I is current in milliamps
See page 301 of "Noise Reduction Techniques in Electronic Systems" by Henry