The “normal” is 1m squared by default.
So, if your grass mesh is smaller than that, you can basically guarantee that it will fall outside of the tile and not be precisely aligned.
The thing is it really doesn’t matter.
Proper grass will be longer and dip under the landscape / grow above it as needed via vertex displacement.
Proper vegetation will also grow towards the light vector, which is now possible since the sun/athmosphere updates provide a light vector in materials.