SSB  Bandwidth   and  Courteous,  Channel Spacings 

The suppressed carrier frequency is off set about 100-250 hertz at -5 Db. to place less energy in the opposite sideband yet still allow enough lows to be transmitted for most males. The band pass, at top, above -70 Db quickly becomes very wide. Therefore if we are estimating how wide someone's transmitter is we should reduce his maximum signal into our receiver to around S9 + 20 Db. or less to compensate for receiver front end overload beyond   -65Db.

In the real world,  transmitted bandwidth  is  even wider, than this graph, due to added inter modulation distortion of amplifier stages in receivers and transmitters.

   Also many filters start at S1, with their band passes much wider than the 2 KHz graph sample. Such as 2.4 - 2.9 KHz wide with a shape factor of 2:1, widening to a width of 4.8 -  5.8 KHz at S9+20 Db.

A shape factor graph for two 8 pole, 9 MHz. crystal filters

    If there were two SSB stations S9 in strength and only 3 KHz apart,  both of them are just starting to transmit garbage into each others adjacent channels. If they were both S9 +20 Db. they would be sowing a full 1 KHz. of garbage into each others adjacent channels. This is a guaranteed method to start arguments. If only we could allow a full Kilohertz of channel spacing ( a channel every 4 KHz. ), there would be fair starting points to then discuss abnormal adjacent channel interference.    

    Courtesy requires transmitting a strong signal that is easily copied over lightning and other man made noises but not into our neighbors channel so as not to fatigue the listener. Quite often our transmitted signal would be stronger than S9 +20 Db. at various receiving locations, which makes an even stronger need for some extra margin of spacing.  See Ham Laws.