Good morning,
The 0.4 x 11 are just washers, partly to adjust the hieght of the stack (?), partly to provide a hard base tor the stack against the alu valve holder (?). I´m not sure, really.
The 0.2c10´s are the clamp shim, which dtermines the solid "post" of the stack and has a huge influene o the stiffness of the stack. Most Showas with a 10 mm cartridge rod uses a 9 mm clamp shim, either 2x0.2 or 1x0.3 mm.
The 11 pcs. of 0.15x17 mm shims are pretty normal fora Showa, maybe on the stiff side.
I am in no way an expert on this, and most of my experimenting has been on my Öhlins forks since they are much easier to work on (cartridge go out the top with the forks on the bike, and (most) of the oil remain in the forks).
For what it´s worth, I would try the following (if you want it softer):
1) 9 mm clamp. This will make the whole set-up softer, but will not really changfe the nature of the shim stack;
2) Try a cross-over shim below the first 0.15x17 (aka face shim), 0.10 mm thick and maybe 11 or 12 mm diameter. This will allow the face shim to bend slightly before the rest of the stack comes into play and will provide some softer initial action. It is possible to play with the position and diameter of the cross-over shim. If you should want to try a thicker cross-over shim, use several (I would say max 2, actually), since 2x0.10 is softer than 1x 0.15, and much softer than a 0.20 which would add to the general stiffness of the stack.
3) Remove a 0.15x17 or two. I´m not sure you would notice much difference unless you remove several, and that might then be too much ..... don´t know, really.
4) As a guide for option 3), use the Raceteh system (as discussed earlier, I think), to determine how many 0.15x17 shims you should use on top of the smaller shims in their tapered stack. The Showa big-port piston is similiar enough to the Gold Valve for this to be a reasonably good guide.
Be very careful with any Loctite if you use that on the valve holder nut, and clean the threads thoroughly of any old Loctite ....
Kind regards,,
Torbjörn.