I found 2 interesting links:
- https://www.strymon.net/faq/how-do-strymon-pedals-receive-midi-messages-sent-via-14-trs-midi-cable/ where Strymon describe just what you said. Which means Strymon pedals are bi-directionnal with midi jack. However in the Riverside and Iridium manual, I see that midi out is configurable: ON (pedal can send internal datas) / THROUGH / OFF (which is the default).
- https://www.strymon.net/midi-control-sunset-riverside/ , Hugo (Strymon’s customer support manager) wrote in the comments " As for MIDI IN and OUT, this is done via the EXP jack with the pedal receiving (MIDI IN) MIDI messages at the TIP and sending MIDI back out (MIDI OUT) at the RING of the TRS connection. As the Strymon MIDI EXP cable does NOT support bi-directional communication, you would need to get a device that accommodates for MIDI IN and OUT using a single TRS cable such as the Empress Effects Midibox2. "
-> Strymon MIDI EXP cable does NOT support bi-directional communication
My conlusion is that if The Strymon pedal is set for midi out configured as ON or TROUGH it is just like you said (TRS ring is the TX). If it is configured as OFF it is just like I said (TRS ring is the 5V power supply).