In Web Config, you can register user-defined sizes for the originals you want to scan.
You can load these registered user-defined sizes by clicking Get from User-Defined Paper Size List(Original) in Presets or User Default Settings in Web Config.
Access Web Config, and then select the Scan tab > User-Defined Paper Size List(Original).
Select the number that you want to register, and then click Edit.
Set each item.
Click Apply.