Header image and columns always 100% width

Hello,
I'm trying to create an Excel file containing:

For printing purposes, I'm using in Page Layout > Scale to Fit the following settings:

Problem is: when columns width is increased, then rows and columns scale correctly to fit the page width, while the header image stays the same.

I've seen other persons had this issue, but I was not able to find a solution to this.

Basically, I'd like to always have header and columns fitting 100% of page width.
Thank you

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