how to change default paper size for scan to document

Hi, I do not see this issue answered in past questions.

Being UK/Europe our paper size is almost always A4.

Whenever I scan a document on Acrobat, it presents 'letter' size as the default size to scan to which crops either top or bottom of the document scanned.

I know how to change the paper size and have read Scanning Letter size document results in Legal size PDF | HP | Adobe Acrobat.

Surely I do NOT have to select another paper size to 'letter' EVERY time I scan.

I set up a custom tool to scan to pdf so I can quickly scan rather than all the tiresome selections from File/Create/ etc. But selecting that auto puts it to scan 'letter' size.

I used File/Create/PDF from scanner/Presets and set paper size to A4. This makes no difference to the scan from custom tool.

I used File/Create/PDF from scanner/Custom Scan to set to native interface and product the printer interface when scanning. This only holds for one scan then resets and makes no difference to the custom tool for scan.

Surely, surely, you allow the default paper size to be set to A4.

Hoping for a positive reply. I use Windows 10

Rgds Jonathan