the empty portion below always remains!It seems obvious that it fills the wider space. in this case the height.
If you had the two sided cartilages instead of overlapping you would have filled the width and would probably remain two bands above and below
The curious thing I found out is that:try dragging the explorer/preview division line to the left

autocad inserts a preview in the file (which is what you see).
This preview, for reasons of file size is obviously risicata, so you can put the resolution you want, if the pixels are not there in departure, you will never see them.
but I modified the preview resolution, but it does not change from 512 pixels to 1600 pixels.. .
yes exact in optionsin acad? Did you change the acad preview resolution?
I imagine that you tried to answer only yes, but it was not accepted because minimum 3 words are required.yes exact in options
Do you know about that format?But did you notice that it doesn't make it bigger than 256 pixels?