Rashi -- D"H'em megula mikstasa' Rashi states that no tiltul min hatzad exists when you remove the object from the teven if you can reach the object directly.
The gemarra continues, concerning the case where the object
is completely covered that R' Nachman must hold "tiltul min hatzad lav shmai tiltul" because he poskens like R' Elezar ben T'dai, who permits removalof the object with a long sharp implement. It seems
then that we should infer from the Gemarra that the machlokes
between the tana kama and R' Elezar ben T'dai, at least
in the hava a'mina, is whether "tiltul min hatzad shmai tiltul" or not.
How can this be correct? If the Tana Kama agrees in the reisha that
"tiltul min hatzad" doesn't exist when the object is only partially
covered? What is the difference between teven falling off the
object upon removal when the object is partially covered or
when it is completely covered?
Rashi's intention, when he explains how the item is lifted (and says that "there is not even Tiltul Min ha'Tzad) is that the item is resting in such a way that half of it is exposed and one is able to take hold of that half and to pull it towards him, without lifting the straw that is on top of it at all .
This is not the case with regard to the radish that is buried with its wide part below and the narrow part on top, in which case the dirt is resting on top of it and he has no choice but to lift the dirt at the moment that he removes the radish from the ground, and let the dirt slide down.
M. KORNFELD