SENSOR_A by default is connected to the ENVELOPE (E) pin of the TS4231. And, the SENSOR_B is by default connected to the DATA (D) pin.
There is also the ability to swap the E and D pins on a per sensor basis in the JSON file.
JSON File Snippet:
The parameter, "sensor_env_on_pin_a" is a 32-bit vector which allows you to swap the location of the ENVELOPE pin on a per sensor basis. As shown in the example above, all 32 bits are set to '1' meaning that the E pin is on A for all 32 sensors. Setting any of the 32 bits to zero would then swap E to SENSOR_B and D to SENSOR_A. This feature is to help with flex layout because there may be some cases where you need to swap the E and D pin routing for the most efficient layout.