Well, I think you only talking about struts. They are that long to get from the bottom of the spring down to the lower suspension arm.
Rule of thumb is that the minimum extended length of a shock is around 2*stroke +6 inches, overall, ie 16 inches in your case.
If you draw the shock in the extended and compressed position you'll see why.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.