Jordan covered the math since neither of us are rocket scientist.
Its not magic. Big turbo or turbo(s) hit late- the later they come in, the less torque you will make. I mean, this is turbo 101 Bro.
Here are a few other LS based examples with larger turbos that come on later than some would like.....
http://i1105.photobucket.com/albums/h344/fbodyjunkie06/S484Tacoma_zpsd24602e3.jpg
From
Or this-
http://ls1tech.com/forums/attachments/forced-induction/410350d1373952657-stock-bottom-end-lq9-930whp-17psi-91mm-garrett-930whp.jpg
From
(on lower boost this run)
And one Example of a turbo set up that would send a rod out the block first pull. Similar HP to whats above, just smaller turbine/ar that hits like a freight train. Same power, much different torque curve.
http://s152.photobucket.com/user/rotary1307cc/media/162_zps18b4e8ec.png.html
Soak it in, because knowledge is power!