You need Saulgoodes overlay bg script to add reflection to the image.
I can not get GAP to work correctly in Gimp-2.8 so i just use Map Object.
One seamless 370x370 tile and map orientation 15 degree intervals up to 180 (12 layers).
You will keep having to duplicate your pattern before each map and place it on top.Then duplicate layers from layer 1 to about layer 12 and place them on top.

Then i added a white glow with a blur for reflection.Then set it's opacity real low.Place it as the bottom layer (bg layer)
After that run Filters>Animation>Overlay Background.
And it's all done. This is an animated PNG so if you can not see it try the FireFox browser.
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196_MyMapObject.png [ 571.47 KiB | Viewed 336 times ]