So, I worked with Voipo support to have the "Outgoing Call Without Registration" set to "NO" on both FXS ports. I had to actually call them and they had to remote into my network and then into the ATA, but once there, the change was quick and easy.

I'm happy with the result, since if the ATA loses registration, I now know it as soon as I pick up a handset.

Quite honestly, I'm surprised that this isn't the default behavior for Voip.

Trich, thanks for pointing all of this out!