Placing a wall (2) above another wall (1) will remove the top facing texture of (1) and the bottom texture of (2). The rotation doesn't matter, it can even be rotated 180° so the models don't even touch each other.
Examples:
90° Rotated with 4-1-1 and 4-1-3
90° Rotated with 4-1-2 and 4-1-3
180° Rotated with 4-1-3/.../11 and 4-1-3
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Affected blocks:
- 4-1-1
- 4-1-2
- 4-1-3
- 4-1-4
- 4-1-5
- 4-1-6
- 4-1-7
- 4-1-8
- 4-1-9
- 4-1-10
- 4-1-11