Solved, the size of the annotated diagram is static (like set values).
I didn't really have time to solve stuff so i fixed this way:
In the file: <xerte install dir>/modules/xerte/parent_templates/Nottingham/models_html5/annotatedDiagram.html
Below line 85 I added this:
Code:
imgMaxW = $x_pageDiv.width() / 2;
imgMaxH = $x_pageHolder.height() - parseInt($x_pageDiv.css("padding-top")) * 2;
Yes, it is still not responsive, but it does what i need it to do.