anatomy of Kohler handheld showerhead – flow restrictor

I have a Kohler Flipside handheld showerhead (K-17493), rated at 2.5 gallons per minute. But the actual flow from the showerhead is under 2 gallons per minute. The problem seems to lie with the showerhead itself: when I remove the showerhead and hose from the shower wall and turn on the water, the flow is much stronger.

I've checked for debris, and it doesn't seem to be a problem. (The showerhead is new.)

I would like to remove or adjust the flow restrictor in the showerhead to permit a stronger flow. But the instructions that I've seen online that apply to other showerheads don't seem to apply to this one — or, at the least, I can't see how those instructions apply to this showerhead.

Here is a picture of the inside of the showerhead:

Many online instructions suggest that an O-ring be removed. In this case, is the O-ring the yellow disc? It is protected by the metal ring above it; is there any danger to breaking that metal ring so that I can remove the yellow disc?