Spotting Ships

[kennonlightfoot]

Surface ships sent out on Raids seem to be almost invisible to Fleet ships. I have noticed that attempts to engage sometimes get a "+1" result which I believe has something to do with spotting.

Does anyone know if these "+1" results accumulate during the current turn and improve the chance of other attacking fleets getting a hit?

Also, do different type ships have different abilities to spot and be spotted?

The manual talks about it but gives no real information on predicting the out come.
It says that fleet size affects spotting but apparently not much. I have had stacks of 9 not able to find an adjacent combined fleet of four German and four Italian ships when they are in Raid mode.