I know this is an old post but does this statement from Rinnai classing it as a combustion inlet for an appliance mean there is only 500mm needed from the regulator vent ?. I come across a lot of installations where the bottles are just to the side of the infinity

https://rinnai.co.nz/attachments/docs/vent-terminal-location-as-nzs-5601-1-clarifica.pdf