I guess two dollar answer is yes. However, what does clock test say, was a combustion analyzer used. Than the what if's. What if orifice size need 4" to provide rated input. I don't think I would adjust reg without at very least clocking meter. Also probably would check for orifice blockage. Several years ago I got tricked into thinking a water heater was overgassed by the clock test. Reduced input until flame was pretty low. Didn't look right, but left it that way. Few days later we get a gas leak call there. Seems there was, If I remember correctly a 12cfh underground leak. That meant I left the awh 12cfh undergassed. Dumb move. What I should have done and always did do except that time(I was assisting a rookie & made a rookie mistake) was to spot the meter first to determine only pilot flow existed, before clocking appliance
I guess I agree with you to a point. I agree that the amount of gas being actually used is the firing rate, but I also believe the pressure could play a part in determining it. If you raise the pressure, should it not force more gas through the orifices? Wouldn't that raise the firing rate? Now, I am thinking the btu conttent of the gas would determine if we were actually overfired yet, but it could happen that way I am thinking. I have read the btu content of natural gas varies in some parts of the country, so I am thinking that could play a part in it too. So, I don't think gas pressure alone is enough to answer your question.