How to prevent jQuery BlockUI Dialog from extending

How can I prevent jquery blockui dialog from expanding? i thought draggable: false? but it doesn't work.

// this is essentially the default dialog if not overriden
    initDialog: function(e) {
        // modify timeout to do jquery dialog
        if (typeof jQuery.ui != 'undefined') {
            var _session = this;
            $("#" + this._clientId).dialog({
                autoOpen: false,
                bgiframe: true, draggable: false,
                modal: true,
                buttons: {
                    Ok: function() {
                        $(this).dialog('close');
                        CallServer();
                            }
                }
            });
        }