Hi — thanks for reaching out!
I took a closer look at this, and the behavior you’re seeing is expected.
Voicemail detection and drop are designed specifically for outbound calls, where the system can detect whether the call is answered by a person or a voicemail system and act accordingly.
For inbound calls, this feature isn’t supported since there isn’t an external voicemail system to detect against. Instead, inbound flows are typically handled by the assistant directly (e.g., answering, recording messages, or routing the call).