yeah, my Wossner pistons are exactly as you described,,hence why i previously asked about markingsI think you can rule out Wossner, they are nornally stamped with a long number ID number.
The Wisecos I had were flat but if you look for pictures of different c/r Wiseco FTE they do look similar. Assuming it is not just generic pictures.
Ross pistons used to be quite popular, they are stamped Ross underneath.
JE do make FTE pistons but not that popular from what I can remember.