I'm thinking top means cylinder head side, not slot position but I could be wrong. The taper on the inside top is designed to take combustion gas pressure and apply an outward sealing force. We rebuilt Quincy compressors at the nuke plant I used to work at and they described that in their manual and in Quincy's case, they had the dot on the top. They called the dot a "pip". I don't know why one ring would have a pip and the other say top unless maybe that is supposed to be the top ring for that set?
