I've got a pretty good preliminary idea of how the coordinate system works for the LDP-1450, at least the relative coordinate system.
The difference in each coordinate step is 25% of the total character size. So if one character is 32 lines tall (which it is without any scaling), then a vertical coordinate of 0 will show no portion of the character, a vertical coordinate of 1 will show the bottom 8 lines of the character, vertical coordinate of 2 will show the bottom 16 lines of the character, etc. NOTE that coordinate 0 will show the bottom grey part of the character if the shadowed edges are enabled, but otherwise will show nothing. This may be an unintended design flaw.
Horizontal coordinates are the same idea but it is more difficult to represent them as pixel shifts since they don't map 1:1 to pixels. We can safely say that incrementing the horizontal coordinate by 1 will shift all characters to the right by 25% of their total width.
I am pretty sure that this is true no matter how scaled the character is (ie it remains a 25% step) but I have not yet had a chance to verify this.