How can I control the size of the 'full screen expand' window?

Hi there

When I open my uploaded MP4s on my desktop, they expand to the allotted size (640x360) and play nice and sharp.

When I press expand on the bottom right of the same video once it has uploaded to the Flowplayer window, the full screen size renders the video fuzzy.

Not nice!

Any ideas about where I go to control that setting?

Thanks
Derry