This has been bothering me too. So... solution!
Here is a link directly to my PostImage repository so everyone can see the images in FULL resolution.

https://postimg.org/gallery/1v2m10jn8/

In the latest pics, notice the progression of change in the square test pattern pictures. See how it moves closer to the center as I rotated the Galvo. Image 126 shows the change really well (overlapping squares).

Pictures 129 through 135 show the hourglass pattern as I increase the speed of the laser drawing. The first is at 100mm then I increment by 100 for each additional pic up to 500mm (132 & 133 are both set to 300). You can see the edges smooth out and the center pull apart b/c it's drawing too fast.

Pic 136 is an interesting one using the spiral test pattern. The sides are clipped and there is a chunk out of the right side. I think I need to change the Height calibration in the software and the chunk is probably a thread getting in the way of the laser.

J