Boot door full of water

[Simon Wallwork]

Thinking this through a little, I wonder if the boot interior is actually at a little bit of low pressure, due to the A8 aerodynamics?

It's quite possible that a low pressure area forms behind the car at speed, causing air inside the boot to leak out- lowering the pressure within the boot and sucking water in through any available wet area.

I know mine was the grommet under the leading edge of the boot door, but why water would choose to go uphill into the boot door, when it could go down into the gutter is less clear.