Mark a cell with a RadioButton to "checked"

I have a column with a RadioButton in each cell. RadioButtons are added with AddRadioButton(0,i,False).  SetRadioIDX(0,i,0 ) does not cause a radio button to be 'checked'. 

How do I set a cell's RadioButton to "checked" if not using SetRadioIDX ?
What is the last parameter, IDX, do ?

You can use