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Regarding the first question (if it's still relevant): grass doesn't always appear; it only appears as a distinct border, for example, when using a rectangular brush size. But you can set the size to 1 or 3. Then the border will be smooth, and the more you hold it down, the clearer it will be.
Froska, you also helped me with ArmySlots. Thank you.
Akat, regarding the last point... A script definitely won't help you here. You can reduce the effect by properly configuring the terrain; then the camera might become less free. Or redesign the game ;). But that's all.