From description, Use Coordinates evaluates the texture using
target coordinates in the local space of the force field object.
2D is supposed to ignore the Z coordinate. Thus one would assume
that if both are enabled, the force field effect would move with
the force field object, and Z would be 0.
However, instead first the 2D option projects points onto a plane
passing through the global zero and orthogonal to the local Z,
and only then the resulting point is transformed into local space.
Z is not locked at 0, so procedural textures like Spherical Blend
don't work as expected.
To fix this, apply local transform first, and then just clear Z if 2D.
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