ion-radio: Not able to get the value selected to populate in form

I have the following pen to illustrate my problem. I want users to be able to select a Shirt Size and I want to capture the selection on the main form ("Sample Form")

Open the codepen below and on the left menu select Form, enter first name, last name, and then tap below the Shirt Size to see the list of shirt sizes.

http://codepen.io/gigocabrera/pen/MwKPKr

How can I get the selected shirt size to display on the Sample Form?