Never seen a statement specifying 13" WC for ANY RV absorption fridge by ANY mfg.
10.5" to 11.5" operating range for water heaters, stove top burners/ovens & fridges etc
Orifices have been designed for this specification in order to properly mix with air supply (fuel/air ratio is very narrow)
Where did you read this 'Norcold specifies 13" WC requirement'?
Got a LINK
Biggest issue with absorption fridge cooling abilities are due to RV MFG NOT properly installing them (tight clearances/proper draft--air flow) as required by the Fridge MFG.
BTW......11" WC is standard for residential applications also