I never quite got the distinction. E.g. in BOS both the SEN and C side had absolutely the same interior and food. In German outstations the food on the SEN side seems to be a bit better in gernal, but e.g. the Tower Lounge in Frankfurt shows that combined lounges work. Having just one kind of lounges below the FCL would certainly help balance people to wards the closer and/or less crowded lounge.
what would distinguish FTL and SEN then???
Personally, I find the tower lounge to be below the level of the JFK SEN lounge, for example.