Confused by back plate graduation

[4Strings]

I am working on my 2nd IV kit and am confused by grads given in different places. I know I am supposed to just "use the force" in arriving at plate thicknesses, but...In the Ultimate Siminoff book, drawing #13 shows max back thickness of 0.25" (6.35mm), significantly thicker than the 0.20" (5.1mm) given for the top plate. Yet, I thought I had read that the back plate was actually supposed to be thinner than the top, due to its greater density/strength.

Can anyone shed some light here? Also wondered whether anyone would share the grads from the Stew Mac A5 plans. Is there any reason to buy the Stew Mac plans if I have the Ultimate Siminoff?

On a related topic, can anyone point me to some good web images of mandos which illustrate the recommended recurve.
shape.
Thanks in advance, Brad

[buddyellis]

Back thickness near the neck block IS significantly thicker than anywhere on the top, but you're not going to get that thickness on an IV kit probably. The rest of the back is usually somewhat thinner than the top.

Theres a map and discussion of loar specks here.

P.S. make sure and keep the thickness at the tailpiece > .120 as this is an area of significant stress, and the IV wood is not terribly stiff. Thicker is better in the area that is under the strings.