Watch it over a few days. What you’re seeing maybe normal vatiance due to temperature changes and BMS irregularities. Many times I’ll charge at night (cold) to a certain percentage but when I actually drive it in the afternoon the next day it has dropped 3-4 percent. But that’s not due to phatom loss, but temperature and BMS fluctuations. You may even see an increase in charge level without even being plugged in depending on what time you check during the day.
As had been said, the best thing to do is check if it’s sleeping or not. Third party software is the most comprehensive way of doing this but you can look at it yourself by using the Tesla widget. When you look at the widget in the lower right will be the last update. While it’s sleeping that number will grow to hours and perhaps days. Of it’s always low, you are not sleeping. It’s not fool proof as phone connectivity and OS restrictions on when it’s allowed to be updated vary but it’s a good indication.