Further to my original question . . .
I've been foraging around and discovered the dnnModal function in dnnModalPopup.js has a parameter, isMaximized.
I've tried stuff like this but to no avail I'm afraid:
string[] Params = new string[] { "isMaximized=true", "tid=" + this.ModuleId.ToString()};
lnkEdit.NavigateUrl = EditUrl(string.Empty, string.Empty, "Edit", Params);
I guess that would be a step in the right direction if it worked, would still need to remove the top and bottom space, that looks like it's hard coded in the script.
But I'd really prefer to use the full screen width and height, i.e. no browser menu, toolbars etc.
Best Regards,
Steve