This can be done, however it requires you generate the size image you want on a 1280 x 720 backdrop an place your image where you want it to appear on the screen.
So, what you will want to do is to generate a 1280 x 720 blank image, then using you @@preview line for reference, place a 565 x 317 image on your blank bacdrop at postions x=680, y=270. Something like this image HERE.
Then when your backdrop is displayed the HUB will crop everything but your the image.
Now i have another problem ,i try thumbgen designer did my template and i put the file into template folder and its doest not show up in thumbgen even if i refresh. i also notice that some template dont work ,like dribler mega pack its as a empty template
that dont work!!
Why it look so easy nothing to put on that template
I have start from the template wd original look std and delete almost everything and keep the fanart and place it where i want ,save it in template folder ,start thumbgen and nothing there !!