Why scene->overlap() does not return face indices?

I would like to get the actors and faces indices intersecting a convex geometry, I use the following code to overlap a convex mesh over a scene:

[...]
        const PxU32 bufferSize = 256;        // [in] size of 'hitBuffer'
        PxOverlapHit hitBuffer[bufferSize];  // [out] User provided buffer for results
        PxOverlapBuffer hits(hitBuffer, bufferSize);
        PxQueryFilterData QueryFilterData(PxQueryFlag::eSTATIC | PxQueryFlag::eDYNAMIC);

        bool status = scene->overlap(geometry, pose, hits, QueryFilterData);

It returns hit results with actors, but all face indices equal to -1. Why?