I've got a link which opens an 'External site (in a lightbox)' I've set my lightbox height to be 940 x 880px,

This looks fine, but then I have a hyperlink form this lightbox which opens another page in the lightbox window but I need the lightbox to be shorter (940 x 700px) otherwise I get ugly gaps at the top and bottom. Is there a way of changing the size of the lightbox window here?

I have tried using 'External site (in a lightbox)' instead for the hyperlink so I can set new lightbox dimensions but it still inherits the original lightbox size.

Thanks for any help
Corrie