Grease Pen settings

Hi everyone, wonder if you can help me with this?

I'm using 2.82 with grease pencil with a view to roughing out some retopology but I've gotten stuck.

I'm struggling a bit as the object I'm drawing on acts like it is on x-ray mode, so I see the lines I've drawn on the rear faces through the object I'm drawing. 

Even if the lines to the rear face were faded or thinner it might help me. Maybe I just need to use the layers to hide the rear lines?