Size variation depends on the load as well as the gas analysis.
With poor gas quality de-rating might be an option. Factors such as temperature, altitude, and gas quality can all derate generator output. Site testing with load and computer analysis is the only way to confirm generator size.
The customer is responsible for providing a flow line to deliver sufficient gas flow and pressure to the specific area the machine will sit.
At the end of the flow line there should be a shut off valve with NPT threads 2″ minimum 100 PSI maximum.