It was kind of you to make his obesity fake. I don't like Vetinari very much - not so much /like/ him, as intellectually appreciate the idea of a benevolent Big Brother - yet my faulty sixteen-year-old female mind couldn't stand the thought of his actually being fat.
Anyway, this story is a marvel (urgh, almost spelled that "merval" and then "mavrel"), a completely in-character but completely unexpected explanation. "The essence of Deep Sea Bloatfish" - that's stored in my headcanon now. :)

I read this awhile back and didn't comment on it, but it's absolutely brilliant. This wonderfully explains how Vetinari could be the obese Patrician of the first novels. I like, like, like. There's always something to think about in Vetinari's rise to power.

"Doctor Follet had not been thinking entirely logically here. He had failed to understand that while an Assassin's body is important as a working tool, there is a far more important and essential one between the Assassin's ears, one that remains untouched and unseen behind physical obesity."

A very common misapprehension - but one that Vetinari frequently took advantage of. Lovely little story - is this a one off or going further?

Oh very clever, you've got round a continuity snarl up very well. You could send the idea off to pratchett himself.