I’ve looked, but didn’t see this. What is the origin point for the x,y coordinates. If I want to place something at, lets say 3", 3" using the ruler is it from the upper left, lower left, or the right? I would guess upper left, but I’ve seen advice to position at lower right.
I use Inkscape so my answer may be specific to it’s positioning system. If I place something in my Inkscape 0.92 design at 0,0 it will appear in the GFUI at the bottom left-hand side. This is consistent with the x-ruler in the GFUI, but inverse to the y-ruler. Also note, that the design will be outside of the area the glowforge can actually lase. It needs to be moved over a quarter-inch or so and up a little over an inch.
You can orient your artwork with the measurement and placement tool. Using this tool, you can choose to orient to the center, upper left, lower right, etc.
In my opinion you’re just going to fight frustration with that plan.
In Inkscape, or your design tool of choice, place your coaster design inside an outline of your coaster. Make the outline its own color.
Place a piece of cardboard on the bed of your glowforge. Gently secure it so if you bump it slightly doing the next steps it won’t move.
In the GFUI set everything to ignore except the outlines of the coaster(s). Cut them and remove them from the cardboard. Place your coasters inside the outlines, set the outline cut to ignore and proceed. You can engrave coasters pretty much forever. If you want to do different designs, just use the first design as your template. Each file you load will be perfectly placed relative to your cardboard jig.
Presumably you will eventually lase something besides a coaster. At that point to make more coasters just get a new piece of cardboard.
On mine I cut and installed the honeycomb tray boots to eliminate slop, then put down blue tape on the bed near the edges. Then placed single vector line cut as far out on each of the four sides as the GFUI would allow. Now I have a visual in the bed for my exact useable space.