Thick Hair - Flat Iron Temps.

I have very thick coarse hair, when I have short cuts it poufs out more so I'm growing longer. Question: I have a ceramic Paul Brown. What temp do you put your iron on? I have the setting on 320. I'm too nervous to put higher but as you can see from pic. doesn't flatten all those thick layers. Plus I use alot of conditioners, frizz products, heat protectors etc.? I'm new to this forum.  I'm open to any suggestions. Thanks in advance.