Avatar IV API results different from studio

Hi.

I have a technical question about the Avatar IV video API Generation. I am a heavy user of the classic video API, but when trying the Avatar IV, the videos are:

getting a different aspect ratio as expected (I am sending a portrait photo and sending portrait as a parameter, but the video is square)
the video is getting the background removed. Can you please help me with this?

When I create this at the Avatar Studio, the result is ok.

Also, can I use an avatar id of my account instead of uploading a photo asset to create the video?