I have the same problem as Bob Low and apparently hundreds of other people as indicated by a web search that I did. I didn't see you reply to Bob but your answer to the other person seemed to be extremely well thought out and knowledgeable. Do you have any idea why a toilet bowl would not fill completely up?
My research shows that buying a new toilet and having a new Flow Master mechanism does not solve the problem for the majority of people. The other plumber's answer about fill holes plugged with hard water sediment is smart but in the case of a new toilet, doesn't solve the problem.
Is there a more global component to this system that might be at fault such as vents on the roof or something else???
I have the problem with both toilets in my house and they are back to back on the wall.
Your answer would be greatly appreciated as this has a been a daily annoyance for 10 years. It is also embarassing for guests when they have to ask for a toilet brush since there is not enough water to clean everything out. That is right - this problem has resulted in cleaning the toilet with a brush every single d**n time it is used! LOL! How I maintain my sense of humor about this I don't know. Thanks for your help!