I'm using bind vops to access primvars inside a materialbuilder. subject is an object copied to points with varying primvars(index, orient,...).
For mesh primitives this works out of the box with either distribution method (pointInstancer, Instanceable Ref., Reference). For volumes it only works with references, not with any instancing method.

here's an example with a) pointInstancer w. meshes, b) pointInstancer w. volumes, c) volume references.

any ideas how to make this work with instancing?