Im glad my scripts worked with you , BREED , and I think what you want is easy to do .
Why don't you place the zones behind the crates you want to sneak behind them , add a waypoint to the enemy so he looks forward in times and back in other times , once he is not looking at the player side you move quickly behind the crates , and when he looks at the crates again he won't detect the player , also if you get out , he will see you , fair simple . And for the FOV , I guess Bugsy answered it fairly obvious .
Cheers
"I am the night visitor when everyone is sleep , and when the last light fades"
The illusionest