Starving a gas heater with insufficient gas pressure will usually cause a "bad flame" which creates sooting, and that interferes with the excange of heat in the coils (the heat exchanger). It also can damage the exchanger.
The specs for the proper gas pressure are in the Owner's/Installation manual of the heater you own. If you can't find it, it's available online. I have seen numerous installations where the gas line is "shared" with the household appliances, to the demise of the heater and it's operation.
Also, please quit trying to engineer your gas pressure, line size, etc., unless you have a manometer to determine your actual pre- and post-gas valve pressure. That's what the gas company gets paid to do, and you want to have them on the hook for performance. If you "advise them", other than showing them the requirements of the manufacturer, you risk being the one at fault for it not working.
I'm sure you will get it done right! Good luck.