Wowser! someone drop in the cliffs notes summary on these...
So there's a few things going on here.
1. You will notice the upper shock eye is mounted on the side of the shock rather than at the top of the shock body. The result is a longer shock in the same amount of space and without relocating either of the shock mounts. The factory shock and all other 3.0 offerings will reach full bump before the axle is anywhere near the frame. This shock will allow the axle to come all the way up, making full use of the available up-travel limited by the distance between the axle and frame at ride height.
2. Anyone with ICON's bump kit right now knows there is a spacer sleeve that slides on to the bump before being installed. What they don't know is that the spacer sleeve design feature was added in anticipation for this system. Now by removing that spacer sleeve, the bump doesn't bottom out until the axle is nearly touching the frame. The height of the spacer basically represents the height of the stock bump stop cup that would otherwise be the limiting factor.
3. The spring is a tad taller than stock, maybe up to an inch taller but it's more like 3/4" on my truck. The added height of course contributes to added up travel by putting more distance between the axle and frame at ride height.
All of these factors combined essentially add 2"+ of up travel and and 1"+ down travel. To put it plainly, you are adding nearly 40% of up travel for a total of 15" total travel. I believe I was told that the kit has a potential for even more total travel, but 15" is what they are advertising as the real world number.
I believe it will allow more travel because when I installed the springs with my "old" ICON shocks, the springs drooped way out to where I had to put a jack under the axle to line the mount up with the bottom of the shock. When I installed these shocks, I had to do the opposite. I had to compress the shock with a jack to line the bottom mounts up. When I stood on my axle with the truck in the air, the springs reached full droop which was not possible with the "old" ICON shocks...or any 3.0 for that matter.