Solution or Workaround
Why does the KEYMARKER legend draw the markers so small compared to the pecified KEYBOX?
Answer:
KEYMARKER symbols are always drawn the size specified for the symbol within the current symbolset.
At earlier versions, the KEYBOX command determined the size of the MARKER as well as the box that represented that symbol in the key legend. This was not a true representation for the symbol; some users needed the symbol in the legend to be the same size as displayed in the coverage. The size of the markers in the legend is now controlled by the size in the markerset. To interactively change the symbol for your key legend display:
MARKERSYMBOL
MARKERSIZE
MARKERPUT