Sent a message to BI support. Ken responded with this.
The "postage stamp" size images come from the DATABASE alerts list. These are used if a hi-res version is not available.
If you want hi-res alerts images:
Enable them on the Trigger tab in camera settings.
Enable direct-to-disk
Enable the pre-trigger buffer at least 5.0 seconds
Ensure the KEY FRAME RATE from the camera is at least 0.25 as shown on Status/Cameras after the FPS.