Custom column formatting: get current folder (for hyperlink with relative path)

I am using this article as the basis for applying custom formatting to create a hyperlink from the field value.

So the JSON for formatting is something like:

{
   "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
   "elmType": "a",
   "txtContent": "Project Documents",
   "attributes": {
      "target": "_blank",
      "href": "='https://crescent.sharepoint.com/sites/projects/' + @currentField"
   }
}

In the above, @currentField is used to extract the value of the current field/column.  

And I see from here that it's also possible to use @currentWeb get the main site dynamically rather than hardcode it.

What I really need is something similar to get the folder for the current item, so that I can for example then refer to a sub-folder relative to the current folder, rather than relative to the top level, i.e. something like @currentFolder in the below:

"href": "=@currentWeb + '/' + @currentFolder + '/my-sub-folder/' + @currentField"

Is this possible?  Or is there a better way to construct hyperlinks like this that are relative to the current item? 

The problem with full hard-coded paths (like the following) is that this formatting trick won't work for any folder, only for a specific folder...

"href": "=@currentWeb + '/Documents/North Dept/Team A/2023/Reports/my-sub-folder/' + @currentField"

And I can't see that using an actual Hyperlink type of column would work for this, because the full path name would need to be used... because it's just a string that is interpreted as a URL?  I'd really like the ability to create hyperlinks that are relative to the current folder.