Do you think that Turbo only kicks in when the cranks are spun above a certain RPM? By dropping several gears your cadence is likely to increase and perhaps once a preset level of RPM is achieved then Turbo mode will engage.I'm now riding a Riese & Muller Supercharger Rohloff and I have found that in Turbo you have to drop several gears to get the full assist. Once you do it's great.
Jim