I think DW has a pretty well designed car park, big fan of angled parking.
Where this breaks down is as always, the user, the human factor.
It would be like if they just opened the gates at Brisbane Entertainment centre and said "have at it peeps."
As has been suggested, simple solution is to have attendants (only needs a small number) directing cars in, and filling each row, one at at a time all the way. When you leave it up to people they will naturally try to go to the next row to get a closer spot to the gate. Don't let them do that.
Yes they will grumble and be pissed for a whole 5 mins when then are forced to go all the way up the back of the first row. But they'll soon forget this after a good experience follows and save a lot of the frustrations that seem to have been felt on the previous night.