That is quite a difference.
There are a few things to check. First look in the camera properties in Blue Iris, on the Video tab. Make sure "Anamorphic" is not checked. Make sure "Area of interest" is not checked.
It could also be that Blue Iris is pulling a different stream than you are seeing when you view in the camera's web interface. Double-check the resolution of the camera reported by BI (should be on the camera properties > Video tab just above the Anamorphic checkbox) and make sure it matches the main stream of the camera. The main stream should be set to the camera's largest resolution choice.
There are a few things to check. First look in the camera properties in Blue Iris, on the Video tab. Make sure "Anamorphic" is not checked. Make sure "Area of interest" is not checked.
It could also be that Blue Iris is pulling a different stream than you are seeing when you view in the camera's web interface. Double-check the resolution of the camera reported by BI (should be on the camera properties > Video tab just above the Anamorphic checkbox) and make sure it matches the main stream of the camera. The main stream should be set to the camera's largest resolution choice.