I think you have the right idea, it's just that your numbers are backwards. The higher the number, the closer you are to detonation. Of course the factory doesn't want that so they are going to set the tune far away from that (11-12.5). The higher the number, the more cold air is being forced into the pistons, allowing for a better ignition, resulting in more power.
The link explains a it of it...
http://www.tricktuners.com/widebands..._explained.htm
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