content: All three of them are misleading, if you expect them to be equivalent to an actual installation.  I have laid some slate, and in an actual installation, the tiles are not supported just on the edges like that- they're laid on top of each other, so there is always at least 2 layers, with a 3" band every row where they're three layers thick.  See this edge-on view.  Slate isn't perfectly smooth, so it's not a continuous contact, and there's a void between the lowest layer and the roof, but it's a lot better than being held at the edges like that.  I suspect the ceramic tiles are similar.  I have no idea how the tesla tiles are laid.  It would be a lot more informative if they installed all three types correctly over a few square feet then repeated that test, since that's the information that's actually relevant.