In the case of teal / green, we have to make choices on what shape to use for a given configuration of corners, and we choose the one which ‘works best’ in most circumstances, especcially in the case of green. Also noting we don’t want to add any new ‘normals’ to the physics geometry, eg in the case of the green with just two opposing tiny corners (near top left of green), I highlighted with lines an alternative shape for that corner configuration which would require ‘new’ normals to achieve. In your image case, the top one (our saddle) I originally did use the right configuration instead, which arguably works better sometmes… but in natural terrain looked horrible as it produced lts of weird rotated square dimples instead of nice diagonal trenches.
We can’t then also have every possible variation of a shape missing those same corners (it’s how the shapes are defined, and it’s how the worldbuilder/lodgen makes use of them, and how chiselling works to get to them), especcialy for green which already requires the full 8bit of shape-metadata we can store in the chunk data to even define the existing set.
The image isn’t missing any for teal though? All the possible corner configurations are there, the ‘low-corner’ (very top) and ‘half-pyramid’ (bottom left of teal) are the end-points where cutting off any more corners would produce just a flat polygon with no depth, and all the others are represented (if you include all rotations/mirrorings which we have)
(Correction: there is indeed 2 more viable teals. Nooooo, I hate implementing teals, missing: take the saddle, and remove one or both of the bottom left/rights)
