OK-I followed the instructions carefully in the link you provided. It turns out that only one of these files is visible at a time in the TM preferences > options window. If the folder is locked, the folder itself shows up in this 'Excluded' folder. If the folder is unlocked, the .sparsebundle file shows up in the "Excluded" window. I hope that is the intended behavior.
My next TM backup started, and is trying to back up over 21 GB again. I started and stopped TM, both with the folder locked and unlocked, and either way it is trying to backup over 20 GB.
I would like to know what to try next.
Also, I am backing up to IDrive, an online backup, just in case there is a theft or fire at my home that destroys both my NAS and my computer. Advice on setting up to avoid these massive backups?
Thanks!