Wouldn't Miles already know what's going on?
As Blanc already surmised, the killer would already know Andi is an imposter.
But doesn't this make things obvious from Miles' point of view? He knows he killed Andi. And he most likely figured Helen showed up dressed as Andi in order to get to the bottom of Andi's death. But also a well-known detective shows up seemingly uninvited as well? I would think it would be pretty apparent to Miles that Helen and Blanc are working together....