wallpaper thumbnail preview size

[Reza Shah]

Hi,

In image wallpaper plugin we can see the preview thumbnail size
follows the active monitor resolution.
So when we open this plugin config dialog in 16:9 or 4:3 monitor, the
preview thumbnails size will be displayed in 16:9 or 4:3 (if
possible).

Which part of 'Image' wallpaper plugin codes handle this behavior?

How can we have above behavior for  'color', 'pattern' or 'animated' wallpaper?
I think it's nice to have same behavior in those plugins too.

Regards,
Reza