This makes the most sense. I have experienced similar things. It's hard to really define; it's just a general stress issue in my experience, and as with you, it was always in non-urban driving. I think the smaller 75 battery has less "sink" to absorb issues; the higher range batteries (85, 100) probably have less of these issues, however, the newer chemistry batteries (90, presumably 100, and presumably all batteries now including my 75) did introduce some limitations.
For instance, I have little idea if the relatively hot (from my usual experience) 80º was a factor in fasteddie7's "general stress" as I most ignorantly put it. Using my ignorance and imagination combined, it's easy for me to imagine a part of the battery heating up beyond threshold limitations without it being easy for the system to cool it off given the ambient temperature, even while other parts of the battery might be just fine. Or, the chemical reaction going on in the cells might have been very particular to that terrain signature that require a very particular fractal response of some sort (as maximum threshold usability), and trying to describe that in any sort of simple way would be foolish; that's all coming from my ignorant imagination. Such as, the terrain signature could cause very particular chemical layerings (at least from an information perspective) in the reactions and chemicals that need particular counterresponses to properly process for further use; since I'm not a chemist, I'm almost certain to be abundantly wrong (or alternatively exactly right and there's no easy way for them to know how to quickly counterbalance the phenomena). I wonder if purpose designed and built quantum AI computers could learn and figure it out, eventually riding along with every Lithium Ion (or other) battery system, eeking out just that much more performance.
I did not know that. I suspected something better was going on with them, though. That's great!