According to a few people, the cuts need to be a tad deeper than the deepest cut ( about a half a cut deeper - so that means a 9.5 rather than a 9, possible if you sit the keyblank on top of a few thin strips of shim in the code cutting machine jaws ).
This, apparently, has the effect of preventing the overlifting of the longest pins ( for the deepest cuts ) during the rapid movement of the key through the keyway, increasing the effectiveness of the action.
Also, removing 0.5mm from the shoulder and utilising a type of buffer ( in the form of a plastic block surrounding the keyblade at the shoulder ) prevents the tell-tale "shoulder dent" found on the face of the cylinder plug - characteristic of bumping.
Just ask Barry the Key!
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