Took me a while to figure it out myself. The Co-ordinates are:

{{Position on graphic in x, Position on graphic in y},{Part of plot legend that should be at the assigned position on graphic}}

So: {{0.9,0.9},{1,1}} Assigns a location on my graphic 90% up the graphic and 90% to the right, and puts the upper right corner of my plot legend at this point.

or {{0.5,0.5},{0.5,0.5}} Puts the middle of my plot legend in the middle of my graphic.

Took me a while to figure it out myself. The co-ordinates are:

{
  {Position on graphic in x, Position on graphic in y}, 
  {Part of plot legend that should be at the assigned position on graphic}
}

So: {{0.9, 0.9}, {1, 1}} assigns a location on my graphic 90% up the graphic and 90% to the right, and puts the upper right corner of my plot legend at this point.

or {{0.5, 0.5}, {0.5, 0.5}} puts the middle of my plot legend in the middle of my graphic.