This is for KS3 ... I can't test it yet if it is the same in KS4.
Set an image res for render on 1000x2000 e.g.
Enable regional render and select a zone you like.
Then before you start rendering, change the resolution to 2000x4000 e.g.
The coordinates don't update untill you toggle the region off/on.
Fixed in KS4 :)
Awesome ... thnx dude ! 8)