I have a similar issue. My drive is in a steepish incline, I drive on forwards, stop on the brakes, pull the handbrake on and release the brakes. After a second or so the hill hold lets go and the car settles onto the handbrake. At this point the car has a real tendency to creep backwards down the drive.
I just leave it in gear. I have zero trust in the handbrake if the car isn't on the level. I'd have to really wrench on the handbrake to hold the car reliably, more than should ever be necessary.
The amount of times I've been fishing around for my phone in the centre console, only to realise I'm moving backwards slowly, I wouldn't like to count.
I live facing down a bit of a hill, at a guess, the car could freewheel to at least 30mph before it reaches the guy at the bottom's driveway. I wouldn't want to have to explain that one...