Kohler One Piece Toilet plumbing
After doing some more research, I answered my own question. Fluidmaster is very deceptive in its claim that their 400A valve "fits" both 1-piece and 2 piece toilets. Yes, it "fits" BUT IT DOES NOT WORK THE WAY IT IS SUPPOSED TO! One piece, low-profile toilets have the tank water level below the rim of the bowl and require a special diverter valve that initially directs water to the rim when the flapper is open and then switches to filling the bowl when it is closed. If anyone is interested, I just ordered one (the LASCO 04-4165 Coast 1B1X) for $22.50 from Amazon.