The contactor in the HV battery needs 12V to close.
Disconnecting the 12V battery or using the green disconnect under the hood cuts off that 12V.
If the contactor was stuck closed you would get a bunch of warnings on the dash.
I did a video a while back about the disconnect
Yes, you can confirm you got it right by driving at 100kph (60mph) and compare with GPS on your phone.
The faster you go at a steady speed the more accurate the phone will be
Steady is the key here
In your case that's a pretty small adjustment, I doubt you will even notice a difference.
If you...
One thing I do when looking for a draw is let the car sit overnight with the hood & doors open with
all the latches closed
Then i plug a thermal camera into my phone & go looking for anything warmer than the rest of the car
Whatever is drawing current will also get warm
Doesn't work every time...