Thanks, my estimate is that the acceleration was virtually maximum. From a full stop no more than 2 metres (6 feet) away the impact crumpled the whole front end of the car ahead.How hard are you accelerating in reverse that your body shifts noticably?
I back into my garage every day in hold mode and it's never come remotely close to being an issue, concern, or danger.
As with you in your garage, I have done exactly (I think) the same thing hundreds of times without any hint of a problem.