Solved, found size constraint located in Joomla: /media/system/js in the modal.js file
/*
MIT-style license
@author Harald Kirschner <mail [at] digitarald.de>
@author Rouven Weßling <me [at] rouvenwessling.de>
@copyright Author
*/
var SqueezeBox={presets:{onOpen:function(){},onClose:function(){},onUpdate:function(){},onResize:function(){},onMove:function(){},onShow:function(){},onHide:function(){},size:{x:800,y:600},sizeLoading:{x:200,y:150},marginInner:{x:20,y:20},marginImage:{x:50,y:75},handler:false,target:null,closable:true,closeBtn:true,zIndex:65555,overlayOpacity:.7,classWindow:"",classOverlay:"",overlayFx:{},resizeFx:{},contentFx:{},parse:false,parseSecure:false,shadow:true,overlay:true,document:null,ajaxOptions:
The change is made to size:{x:600,y:450). In my case I changed it to 800 x 600 and it works.