To simplify my message (me? complicated? surely not!), my interpretation of how the system goes is that non-ramp tiles are consistently flat, with no regard for what ramps border them[1], whilst ramped tiles are selected to match the elevations of all four corners the 'best'[2], with a bias towards having a low-Z continuity in (e.g., as per example above) two opposite corners pinned-High and the other two pinned-Low. And it does this in (mostly?) in quadrants of flatness (but angled accordingly), formed from the X-shape of the two diagonals cutting across the perimeter.
(Is that more simple a description? Is it even accurate? It'll have to do for now.)
When we were still all pondering this, originally, I had played with the possibility of octants[3] and some 'bleed' effects into adjacent flat-ground edges (or even an octothorn/twisted octothorn subregioning) for more fine-grained level-matching, but I think the quadrant version works well enough. It just needs 45° diagonals (and the tile-edge horizontals and verticals), rather than messing with an expanding multitude of 22.5° slope-meets-slope variations, etc.
(Whoops, between that paragraph and the various feetnete, below, I've definitely gone complicated again. But I think it is a complicated subject, and no avoiding that. Definitely when discussing how it could be even less trivial than it currently is ... Not that there's any single good answer to it, but I think what we see is as good as we need.)
[1] We saw with streams, though, that the texture-style for flat ground upon the immediate bank was used to add a 'hang-over' of matching texture-style, rendered above the water's edge tile, e.g. grass stems hanging over, to break up the hard edge. I presume this still exists.
[2] Not sure how the example of ramps would be so touching two adjacent tiles, one low-Z and one high-Z. I suspect it'll be the ramps that would be there if the low-Z were also a ramp... If nothing else, to not have a cascade of earth-reshaping, beyond the single tile you might purposefully enramp/deramp. But I'd have to try this out with Steam version to confirm my prediction.
[3] Either divided with orthagonals and diagonals (N-S, NE-SW, etc) or the panels orientated that way with the dividers at the mid-angles (NNE-SSW, ENE-WSW, etc)
edited to resolve inadvertent bbcode invocation