Writer - Fillable PDF checkbox and radio graphic size can't be changed

Writer - Fillable PDF checkbox and radio graphic size can't be changed

Hi, 

I am testing Writer for the fillable PDF function. I have added Checkboxes and Radio buttons but these are tiny! I can increase the click area using the sizing handles, but this does not increase the actual graphic/icon of the tick boxes and radio buttons? Is this a bug or a limitation of Writer?