Set orientation when creating avatar video (v2) with API

I am using the following API https://docs.heygen.com/reference/create-an-avatar-video-v2

My intention is to get a video in portrait orientation, which is easily possible with the editor. However, when I use the API and I set the following dimensions:

dimension: {
  height: 1280,
    width: 720
}

I do get a portrait orientation, however the avatar is in the middle with white gaps on top and bottom, completely different when using the same with the editor.

Why is that and how can this be fixed? This is a blocker from us to continue working with Heygen and look for different alternatives.

Thank you.