I fought the law and the law won.I use an OGIO bag and just make sure to put the power button up. I have never had an issue with my SP3 being turned on while using this method, but then I've always used this method. It just makes sense that you don't fight gravity. It is, after all, the law.
Not sure if your experience is like mine.
My problem was with the (bluetooth) mouse.
If I left it turned on and if it gets moved even slightly, that triggers the SP3 to wake up.
Similarly too, even if I had turned off the SP3, close the cover and then I pull the power plug, that pulling of power plug turned the SP3 on.
So nowadays, my packing protocol is:
>> slide the pen into the thingy.
>> Turn off the mouse
>> pull the power
>> close the cover and hit the off switch on the SP3.