Although this variation of the exercise provides less range of motion, it allows you to use more weight, which is vital for stimulating muscle growth. (fitnessandpower.com)
A smaller ball will offer less range of motion than a bigger ball. (best-leg-exercises.com)
You will also likely feel less range of motion in the hip when the elbows are on the Bosu Ball, but still attempt to touch your opposite knee to your elbow. (ab-core-and-stomach-exercises.com)