How to paint Space Marine Centurions? 4/4

Amazing set of videos, they are giving me confidence to try things out with my own airbrush,you make it look so easy.
I'm running my airbrush at 18-20 psi do you think this is enough or I should set it a little higher? it sprays fine most of the time but does look to spatter a little on metalics and polyurethane primers. Any pointers would be awsome. keep up the amazing vids and I'm happy I decided to sub to your website better value for money than the new weekly white dwarfs and I learn a whole lot more.

I'm having some difficulty with the playback on this one, thankfully it's just the assembly though.