ag-grid - Set cellRendererParams to data.field items so they are usable in cellRenderer

Question

I am working on an AG-Grid using JavaScript and am having difficulty passing additional parameters for use in a cellRenderer using cellRendererParams and valueGetter.

I have stripped this down to get rid of everything else while I troubleshoot what I am doing wrong.

First in my columnDefs I have these two columns (among others)

{ headerName: 'Test Getter', field: 'subType',
        cellRenderer: LinkRenderer,
        cellRendererParams: {
            isNew: true,
            valueGetter: (params) => ({ sizeL: params.data.size, fileNameL: params.data.fileName }),
        },
    suppressMenu: true, resizable: false, width: 120 },
    { headerName: 'Testing2', valueGetter: 'data.size + data.fileName', resizable: true },

And my simple cellRenderer class:

class LinkRenderer {
  init(params) {
    this.eGui = document.createElement('span');
 //   var ext = params.isNew;
    var ext = params.sizeL;
    this.eGui.innerHTML = `${ext}`;
  }

  getGui() {
    return this.eGui;
  }

  refresh(params) {
    return false;
  }
}

There are a couple things to note in my code to hopefully show some tests I have done to make sure I have access to the data, and do have my cellRendererParams working for non-data strings.

1. The column just below the one in question - that valueGetter is getting the data in those to fields just fine.
2. The isNew parameter that is added first in cellRendererParams is accessible in the cellRenderer and works fine.

I am not sure where my problem is. I have tried all sorts of different things with the valueGetter that is inside the cellRendererParams, and I have tried all sorts of ways to address the fields in the cellRenderer but everything I try returns undefined.

Any thoughts or ideas?