[TYPO3] Increase max. picture sizes at "Resize on Click"-Pop-up

[Markus Eggerath]

Hi everyone,
I would like to increase the maximung size of those images opening in a 
pop-up box. I found this TS-snip somewhere, but it seems to do nothing.

tt_content.image.20.1.imageLinkWrap.width = 960m

I need the maximum picture height to be 650 pixels, but I have 
absolutely no idea where to begin.

Any help's appreciated,
Markus