Why are the SmartSense default cylinder volumes 8.5kg and 3.7kg?

The Australian LPG industry has begun a safety initiative where a 9kg bottle should only be filled with 8.5kg of gas, and 4kg bottles should only be filled with 3.7kg of gas.

This is why the default cylinder volumes in when pairing a SmartSense sensor are 8.5kg and 3.7kg.