Documentation for CompositeField has misleading code in very first example. labelWidth is not a config option of CompositeField and therefore does not change width of labels.

PHP Code:
{
    
xtype'compositefield',
    
labelWidth120
    items
: [
        {
            
xtype     'textfield',
            
fieldLabel'Title',
            
width     20
        
},
        {
            
xtype     'textfield',
            
fieldLabel'First',
            
flex      1
        
},
        {
            
xtype     'textfield',
            
fieldLabel'Last',
            
flex      1
        
}
    ]