With one of my HDMI2AV converters it depends on where the hdmi is plugged in on the port. Try swapping the outputs.
Hope its of help.
Edit sorry I meant HDMI Splitter Not the Hdmi2av converter. Sorry.
Edit 2: Spliter usually clones the resolution from one of the ports to the other. and if the Hdmi2av converter. in on the "master" port the slave port will be at the same lower resolution.