I sorta agree with you but I truly don't know. I seem to recollect somewhere in the book where Mr.B sez something about not changing the amount of lemon. I'll hafta check when I get a chance. What I do remember where there is a variant is in the the Cayenne where he sez a specific amount or "to taste".
I think at least for the first and or second Master-Cleanse everyone should do it by book so they can experience the Master-Cleanse as it was designed to gauge the effects it has on their systems. In my experience and results, personally for >me< I see no need to change it.