Keep in mind, the turbo is primarily spooled by heat waves through the turbine. The more the gas cools, the more the heat pulses disperse... the less reactive your turbine will act.
It's hard to think of, but don't think of the turbo turbine like a water wheel or something that is pushed by a flow of total volume. The turbine needs heat to do its thing.. And sharp pulses of it. Not just a flow of air.