Bear in mind too, not only might signals at 612kHz cause interference, so might signals at other frequencies.
My own technique is to wander around whilst fiddling with the tuning dial. I’m aware that BT OR use it as a kind of reference but to my knowledge, there is nothing that special about 612 kHZ. If you detect interference at some other frequency, that matters too.
Per direction, ignore the extended antenna on most domestic receivers, as that is only used for VHF/FM reception. For AM (MW/LW), the radio usually relies on an internal ferrite rod. Being a ‘rod’, and being optimal when horizontal, the designer will maximise space efficiency by positioning it lenghtwise, side to side, within the receiver. That being the case, for maximum pickup, the radio will ‘face’ towards or away from the source.