I worked this out just now after searching the forum. The Trigger needs a command to activate it, movement on it’s own won’t work, so on the bottom of the Main Map properties: " Key Command to apply to all unit…" I added the command “MoveOnMap” then set the trigger as follows…
“Addspray” is the command to add Spray fire to the Piece. So now, if The Piece moves into the forward Sector with SF, or activates SF while in the forward Sector, it is returned to the original position (SendLocation). This took me all day and I only found the solution by chance on the forum. An obscure box in the Map Properties was the answer. There are too many things like this to remember.
Darren