This seems to be related to which version of Jamf Pro you're on. For example, we're still on an older release and ours is limited to 24 lines. Still woefully small, but a little better than 14. I honestly don't understand why there is any limit at all. I should be able to see the entire script and just scroll my screen and not only see a limited portion of it inside a window. Makes no sense.
The Jamf Pro script editor is both a blessing and a curse. It's great we can make edits to our script and create new ones in place, but trying to use it as a full script creation or editing tool gets frustrating really fast. I never do more than very minor edits within that UI. For any larger edits, I use BBEdit or Visual Studio Code for editing and then copy/paste over the script in Jamf Pro. This also allows for localized testing, which is a good idea before overwriting a script in your Jamf repository anyway.
To be fair, I don't think Jamf ever intended for the built in script editor to be anything but a quick editing window and not intended to be used for major writing or editing of scripts. Still, they should expand the window that we can see the script in at the very least. 14 lines is pathetically small.
This is unfortunately not uncommon with Jamf Pro releases. Jamf seems to have some issue with bug regression in their development process. I did recall this was a problem on some older release, but couldn't remember specifically which one, so thanks for pointing this out. Hopefully they can address this soon.
If you are changing the cut-off options for the finalization when building factory toolkit, copy the cutoff.json.default to your board overlay into file path chromeos-base/factory-board/files/py/config/cutoff.json. Change values in the config file, and rebuild a new factory toolkit. This config file also applies to reset shim.