http://www.goarmy.co.uk/military-clothing/hats-scarves/british-army-camouflage-skrim-head-camouflage-net-prod
Depends what's more comfortable for you, under neath or on top of your hat are perfectly acceptable . On top may break up your sihoullete a bit more, and the brim of your hat will keep it off of your face. They also make good scarves, gun wraps and they're good improvised curtains for a fighting position or snipers den