Size of preview

On my new monitor (2560 x 1440) I´m not able to adjust the to size of the preview to the main window.
At the moment a large area is given away:

Hello,

You are right, we have set the preview maximum size to 1200x1200 for speed purposes.
However now that the machines are getting more powerful we should be able to increase this value.
I will add this wish to our wish list.

Best regards,

ok, thought I was doing something wrong, thanks!