I'm not familiar with your system but there is no passive drain in mid-motors I'm familiar with (Specialized and Yamaha). Bosch or Shimano cannot be any diffferent. The only passive drain is for e-bike lighting but that factor is totally negligeable with the modern LEDs.
With mid-drives we are talking about here it is never recommended to switch the system off for pedalling downhill. You just activate the Off Mode but the system is up and running. The instant current value can be seen in the Mission Control app. (Prior to 2022 models, you could see your own and the motor power in the BLEvo app, and even get the data to Excel post-ride). And that battery draw is zero if you either do not pedal or the Off Mode has been switched on.
It is amazing how much the range increases on long downhill rides! The 2022 Como and Vado are equipped with the new MasterMind TCD display. There is a whole display page devoted to the battery range. Not only the current range is recalculated as you ride but there is a Range Trend data field, too. If you ride uphill, you see the range figure go down and the trend arrow is pointing down. As soon as you start descending, the arrow turns up (I could see that on the 2022 Tero I demo rode this year).
View attachment 109838
The Range data page on MasterMind TCD. The pink colour indicates the Smart Assistance Mode (you enter the distance to be ridden and predicted elevation gain in Mission Control, and the Mission Control automatically manipulates assistance to achieve your goal with predefined battery % at the end of the ride). Of course, Smart Control would make you slower if the objective could not be met at faster pace. (In emergency situations, the user can activate the Turbo mode). As you can see, the Battery Consumption field is null if you do not pedal.
I could use the Smart Control on my older Turbo e-bikes and I only don't have the Range data page in my displays (but I can use the BLEvo app for the same). The reason I'm not using Smart Control is it is me who wants to control the e-bike