I turn on the parking sensors. When they scream, I'm close enough.I got something like this...
... to stop my car in a consistent place in the garage.
(See, for example, https://www.amazon.com/MAXSA-37358-Right-Black-Parking/dp/B000F6DNMQ/ref=sr_1_2?s=automotive&ie=UTF8&qid=1498528007&sr=1-2&keywords=car+stop)
Then I padded everything that the hatch would hit when I opened the hatch, with the garage door both open and closed. Problem solved.