Note that in Sencha Touch's Box Layout implementation, when you give a flex number to the items, the ratio are respected. Three items all with flex: 1 means all their sizes are equally divided. If you want an item to have its natural size, simply don't give it a 'flex' config.
What I want is all of the buttons to have the same size without clipping. It seems in Ext JS that giving flex: 1 would make all the buttons the same size as the largest one and adjust the container. Does Touch not do the same? The parent container definitely has room to grow.