just after i wrote that i went looking for the elusive pump, part numbers are not the same
i did think it was odd, i was mistaking the 040 pump as that operates at 6.5BAR.
if the demand is higher than the pump can supply the fuel line won't be maintaining the pressure, so will drop below the operating pressure that the pump can supply.

044 does indeed flow at 300ltr/hr, i'm full of mistakes today