Alan de G1FXB,
Your correct. any testing and I've done a lot with small loops you need lots of
"shield breakers" or choking to remove the COAX shield as a possible secondary
coupling making it an undesired array and often clouding results or minimally
distorting patterns greatly.
If the RF source is small and self contained it can be at or very near the
feed point and make the problem easier. Same applies for receivers
Generally Loops, large or small, are considered self contained antennas not
requiring ground planes or counterpoises. However in the real world those
will exist. As a result supports or cables and the very existence of the
ground below it do influence the results.