| The pack rack *always* goes so that the rack points out from the seat, not over it.
The "over the seat" option simply refers to the way the bags can be placed either over the seat or behind, depending on if you're carrying passengers or not.
If you haven't got a Ventura bag, then you really should buy one to go with it because it's so much easier than trying to bungee a rucksack or similar to the back of the bike! They really are worth the money once you've used it a couple of times.
Hope this helps, | 
antonye
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