English prepositional phrases What's the difference between in form and on form?

English prepositional phrases What's the difference between in form and on form?

in form
1. (athletes, horse racing, etc.) in good condition; energetic (suitable for work) [on form, on top form, in good (or top) form]
In due (or proper) form
3. In full (or great) form
on form
(athletes, horse racing, etc.) able to develop their own level and in good competitive condition