Splitter in south region of Viewport

I'm creating an app with 4 charts. I'm able to split the charts in the east/west regions using the split: 'true' config option. I want to be able to create a splitter between my bottom two Ext.chart.Charts. They're in a Panel in the south region right now with a splitter (non-working) between them like this:

Code:

var southPanel = Ext.create('Ext.panel.Panel', {
                width: '100%',
                height: '300',
                split: 'true',
                layout: {
                        type: 'hbox', 
                        align: 'center'
                },
                items: [ pieChart, {
                        xtype: 'splitter',
                        width: '33'
                        }, lileastChart]
        });

Splitter in south region of Viewport