Correct. modem_config = 3 refers to Bw125Cr48Sf4096 = 3;. 
Edit:
Longer range (SF12:4096chips/symbol) comes off course with longer TX airtime, and consumes more energy as well (TABLE 1, https://www.thethingsnetwork.org/article/how-spreading-factor-affects-lorawan-device-battery-life). The measurement shows that it takes approximately 25 times longer and 25 times more energy to transmit in SF12 compared to SF7.
Airtimes per 20 bytes: https://www.researchgate.net/publication/339153605/figure/tbl2/AS:857195465957376@1581382733097/LoRa-Chirps-SNR-airtime-and-bitrate-according-to-parameter-SF.png
Maximum throughput:
