Vertical loop success on 500kHz QRP

This evening I've been WSPRing on 500kHz running about 2mW ERP from my thin vertical wire loop with an area of around 70 sq metres. The bottom of the loop just runs along the ground and at the moment is buried in the long wet grass! Despite this, my signal is being decoded in G, ON, PA and GM with best DX tonight 896km to GM4SLV up in the Shetland Is.