I think it is all to do with the active part of the shock
The 1" extensions were added to give an extra bit of ride height.
I do not believe that you would have the same effect by using a longer shock.
Perhaps someone who knows more about the science of it all can explain it a bit better
Here's food for thought .... If the shock mounts have not yet been fitted .... Perhaps it would be possible to extend the mounting brackets by .5 of an inch each !!??
If this was possible you could use the much cheaper standard 13" shock option
