As I wrote in the original thread, voice calls need a synchronous two-way connection, i.e. both parties can hear each other and talk to each other. A voice call cannot have any (significant) loss of signal as you well know from experience - the call drops.
An SMS can be sent or received in a small window of connectivity and with only a tiny amount of bandwidth (160 characters!), and once it gets to the receiver the signal can drop come back, drop again - but the SMS has already been received.
Yes - you need some connectivity for the SMS to get through, but patchy connectivity will do.
Consider keeping the message below 160 characters so it's a single SMS being sent.
References:
https://www.mountaineering.scot/safety-and-skills/essential-skills/mountain-rescue/calling-for-help
https://www.scottishmountainrescue.org/how-to-call-for-help-emergency-in-the-hills/
https://www.thebmc.co.uk/en/what-to-do-in-a-hill-walking-emergency