Sequence Settings from 16x9 to 9x16 / from 4K to HD

Hey Community,

For the first time I am encountering the following issue.

I have a vertical shot in 4K. When I "create sequence from clip", it creates a 4K sequence (in 16x9 because the clip comes as a lanscape aspect ratio when coming out of the camera).

Then I go to "sequence settings" and make it a 1080x1920 sequence to make it vertical and HD. Then I rotate the clip to 90 degree.

Because it is a 4K clip, it should need to be scaled down, but instead, it doesn't fill the frame.

Here is a screenrecording so you can tell me if there is soemthign I am missing.

https://youtu.be/LaMmzAR29c0

Thanks