Bottom line after working with Ken, here's where it ended up... If you have “Use main stream if available” on the Camera>Trigger>AI page deselected, you will get lo-res alert images. Here's Ken's last response to me.
You will get Mainstream alert images if you are using Mainstream with AI. Using these images does use more CPU.
This is something we've gone back and forth on ... currently settled as the way it is now ... save the image that was ACTUALLY used to confirm/cancel the alert. Otherwise, there may be a difference in these because the AI can be configured to analyze multiple images, not just the single alert image.