Karl Beckman WA8NVW - NNV5BH
The fallacy in your example is that WSJTx has no such audio "slot" boundaries, so operator 2 on 1275 cannot be "taking up 2 slots." The audio signal occupies a window from the listed audio frequency to 50 Hz higher, period. We can tell that the authors intended it to work that way by not restricting the starting audio selection to any specific set of acceptable audio frequencies. If you read the user manual you'll find that the software decode process easily separates and analyzes incoming signals less than 10 Hz apart. That's how the "busy" detector works to auto-disable transmit. Skeptical? Give it a try, you'll work more DX without violating the DXers Code of Ethics!
Also note that in your example you choose to set your transmit audio tone anywhere between 200 and 3000 Hz, BUT if your receiver's filter bandpass is only 300 to 2400 (the usual 2.1 kHz filter) you shouldn't expect to see or decode signals much outside that range. You can see this attenuation of incoming signals 'outside the RF filter skirts on the waterfall display. "Split mode" (which in hindsight would have been better nicknamed "transmit tone offset") only adjusts the tone and suppressed RF carrier frequency during the transmit interval. It is not active at all on receive.
Karl WA8NVW OH