Use the cable-run limit and routing requirements for the ETO2/ETF combination.
For the ETF-744/99 outdoor temperature sensor used with ETO2, the linked installation manual allows a cable run of approximately 50 metres (164 feet). Mount the sensor under the eaves on the north side of the building, as directed in the manual.
Route sensor cables according to applicable regulations and avoid running them parallel to power cables, which can interfere with the sensor signal. Connect the ETF to the temperature-sensor terminals specified by the ETO2 diagram.
The manual does not substantiate the old blanket rule of 18 AWG below 50 feet and 16 AWG above it. Have the installer select the cable and connections for the exact sensor, run and local requirements. The longer cable limits for ETOR gutter or ETOG ground sensors are not the ETF limit.
Source: ETO2 installation manual (Outdoor Sensor, Sensor Cables and Wiring).