Question Getting instanced object index in compute shader using inline raytracing?

So my situation is this: I have a bunch of the same mesh I want to turn into instances. Using the RaytracingAccelerationStructure.AddInstances() is working fine
However, my main use for them is in a compute shader that does inline raytracing queries, but I cannot find the api needed to get which instance in the group of instances the ray hits, is this missing or what do I need to do to access this? I need this because I have a seperate array of matrices that map to each instanced object, but I am unable to correctly index into this array of matrices since I am missing the ability to find out which instance I have hit with the rayquery. What am I missing? Thanks!