margins / clipping

[sth0r]

Hello
Iam trying to record a 1080p arear of my 4k screen it needs to be the center from side to side and 2/3 up, with clipping i can get the center on both axes but i would the 1080p area to be a bit higher on my screen see the 2 pictures i attached.
i tryed to play around with the margines but i cannot get that to work...