Vehicle protection

Is there a recommended or required maximum opening between a guard post and wall for vehicle protection for fuel fired equipment in a garage setting?
A townhouse garage has a 70 1/2" opening between the post & wall exposing the furnace & water heater.

Code Check just says Barrier (protective bollards) or elevation reg’d in garage or carports… IRC 1307.3.1 / UPC 508.14

if the code is restricted then dont you go by manufacturers installation instructions