P: Facial recognition reads off of original files rather than previews

Issue: 

• Lightroom Classic Version Number: 12.0.1
• OS Version Number: Windows 11 21H2

Steps to reproduce:

1. Ensure you have built previews for all your photos.
2. Enable "Show photos in subfolders".
3. Select a root folder that contains most of your photos.
4. Press "O" or the People icon to show faces.
5.  Click a person who appears in many of your photos.
6.  Open task manager to see disk activity.

Expected result: Disk activity should be high on the drive that contains your catalog previews file. This would mean that Lightroom uses the previews file to quickly generate thumbnails and search results, especially if it's on an SSD rather than a hard disk. 

Actual result: Disk activity is high on the drive that contains the original photo files. For me, because my original files are on a hard disk, the thumbnail generation and searching of faces is very slow.