The 10 foot section, is that the total length of tubing coming from the gas supply to the end of the manifold? And then does that calculation mean that our line off the supply and including the manifold all needs to be sized at 1-1/4 inch tubing and then reduced from there based on the individual runs?
I make the steel (schedule 40) section the same size (all loads added together and longest run from regulator to furthest appliance, then I size copper based from the regulator to the end of the load I am measuring with capacity for only that appliance