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Algorithm for range warning?

Opinions/knowledge on what the algorithm is for triggering the “Stay below x mph to reach your destination” warning? On current trip my range “surplus” was 50+ miles while the destination was about 150 miles and the “stay below” warning was at 60 and 65 mph. Currently getting message with 172 miles of range and 122 miles destination. This seems new behavior to me; v10 installed just before current road trip.
We just had a trip out-of-state where we ran completely out and never got that warning once. Newest firmware version and on previous trips we'd almost get it too much as we'd arrive at the Supercharger with way more than it said we would. When we ran out last weekend we were 7.6 miles to the next scheduled Supercharger stop. The range showed 13 miles remaining when, without any warning at all, it shut down completely and gave the message that the car was shutting down and to pull someplace safe. We coasted for like a half mile but, being as we were on I70 between Colorado and Utah, there was no place to pull safely off other than the shoulder barely out of traffic. Needless to say this was VERY unexpected and rained on our parade as it set of a cascade of inept Tesla customer service that all but ruined our road trip.
It doesn't use the range, as that's guaranteed to be wrong. Look at the energy graphs and the range remaining on it.

It's a conservative estimate. Basically at the current rate of consumption (i.e. speed) will there be enough buffer (maybe around 10%) to reach the destination. If no, do a little math and recommend a consumption level (again i.e. speed) that will meet the safety buffer.

This behavior has been around for awhile.