I've spent an embarassing amount of time thinking about top down tilemap projections.
45° projection has nice stacking properties and it's used in basically every retro RPG, but I'm doing the dumb shmup trick where I render plan vehicles over a top-down background, which wants a steeper angle.
20° was chosen arbitrarily for the Unity prototype, but you can see it doesn't stack well.
26.5° is interesting; a z-level shift is half the height of the top face. Godot's tilemap system doesn't do arbitrary layer offsets, although there is a proposal for it.
However, if each tile is 2 unit cubes tall instead of 1, you get nice stacking properties like the 45° while being more shmuppy. I am very clever.
