What celestial body (inside the solar system) has the highest flattening ratio? As a planet, Saturn has the highest flattening(ellipticity) which is 0.09796. So, it makes Saturn with the largest equatorial bulge as a planet and as such Saturn is the flattest planet.
However, I have encountered this statement from here:

Earth's Moon is even less elliptical, with a flattening of less than
1/825, while Jupiter is visibly oblate at about 1/15 and one of
Saturn's triaxial moons, Telesto, is highly flattened, with f between
1/3 to 1/2 (meaning that the polar diameter is between 50% and 67% of
the equatorial).

So, Telesto has a flattening value even higher than Saturn itself. I couldn't find any other body that has higher flattening value than Telesto. Does that mean Telesto has the highest recorded 'f' value?
Question: What celestial body inside the solar system has the highest recorded flattening value? Is it Telesto?
Note: Most of the asteroids, meteors, comets and small moons have irregular shapes and as such measuring the 'f' value is impossible and may have no useful value. I want to know which body has the highest recorded 'f' value.
I believe besides Telesto the dwarf planet Haumea in the Kuiper belt could also be in the mix for the highest flattening of objects in our solar system. Haumea is a triaxial ellipsoid where the 'f' value would around 1/2 between the largest and smallest major axis.