A mass flow controller includes at least one conduit having a fluid inlet and a fluid outlet, the conduit defining a flow path along which the fluid flows. The mass flow controller also includes a modified inlet block having an inlet aperture, an inlet channel, and a reservoir fluidly coupled to the inlet channel and the conduit that enhances flow through the controller and improves rate-of-decay measurements. The mass flow controller includes at least one flow sensor that generates a flow sensor signal that is proportional to the mass flow rate of the fluid through the conduit. The mass flow controller includes a control subsystem coupled to a flow sensor and a valve assembly to control flow through the conduit.