Yeah, this is a known issue with the second-gen OEM Bar-Risers.
Some people say this is normal. Other's it seems are not affected.
There are those that do not ride their machine aggressively enough for it to worry them, but for me it just felt sketchy as hell!
It bothered me every time I accelerated or used the brakes........... Mine were as bad as yours. It just felt unsafe to me.
You could try a replacement set of #11, but you would have to rig up some sort of "Press" with some threaded-rod and the correct size sockets or spacers to get them out of the top-clamp.
I went the way of eliminating them entirely, by way of installing very large and thick fender-washers in between the Risers (# 17) and the top-clamp.
This effectively "Locks them out" of the equation, and took care of the flexing entirely.
I bought the correct sized washers at ACE-Hardware. You need ones that have the hole large enough to fit over the center-sleeve of #11 when you assemble everything back together.
Others have done this very same thing to take care of this issue on theirs.
Some have said that you may feel added vibration in the Bars after doing this with the washers, but I've never noticed a difference from before or after. I DO have aftermarket ProTaper Bars on mine.
When I get home from work today, I can post some pictures, and try to see if I can find the size of the washers I used. There are some older posts in the forum about this as well.
Tightening #20 does nothing to fix this, as that is just attaching the riser-post to the INNER-sleeve of the OEM rubber bushing. If you look closely, you'll notice that the inner sleeve is longer than the outer one, and longer than the top-clamp thickness.
All of the flex is taking place between the inner sleeve and outer sleeve of those bushings.
On these Gen-2 bikes, if anyone has ever hauled their bike on a trailer or in the back of a truck, and used the handlebars to strap-down the bike, this puts too much stress on those bushings and will cause them to have too much flex.
I don't ever haul bikes using the handlebars (for a number of reasons) to strap them down, but I know a lot of people who do.
I would suspect this might have been the case with a previous owner of my bike at some point early in its life?