If you arrive in S3, you don't need to take any buses anymore: you just need to walk from S3 until terminal 2F; it's a maximum 15min walk (+ then time to go through the security check in terminal 2F).
You are quite right ^. I have yet to experience an S3 -> 2F International connection, so I forgot about that option. Sorry.
Can you use the walkway for a connection to 2F Schengen and clear immigration in 2F ?