The old "2 to the end" rule (which states you should leave two full number values of adjustment between your DIN setting the the upper and lower limits of the binding, respectively...is false.
While this rule is a fine one to follow, and lends itself to you having a great set of bindings for your weight, the fact is that when bindings are made, they are tested to DIN (Deutsches Institut für Normung) ISO standards.
Basically this means that each setting on the binding has to release at it's numeric retention value. A 6 setting has a certain pressure (weight) that it requires to release...this is true for every value in the scale.
What can and will change (between bindings, and sometimes on the same binding with a different setting) is the "Release Characteristics" of the binding. For instance..say you have an FKS-style 12-DIN binding, and the same model in the 18-DIN version.
If you set each at 8...the pressure value of release will be the same, but the "feel" will be different. The 12-DIN model will have a more snappy, sudden feeling release, while the 18-DIN model will seem smoother, this is because the 12-DIN binding is using more of it's given spring tension to achieve the same release value. The 18-DIN model is at it's lowest setting, therefore even though it's release value is 8, it's using almost none of it's available tension.
Does that make sense?