[quote=@Doc Doctor]
[@MelonHead]

It is still a full force blow.
[/quote]

I don't really see how that would be possible. Lifting a rock up and slamming it back down again is not an efficient action, your character simply does not have time to launch a full force blow -and- avoid the Mech's arm. Maybe if the Mech was a behemoth and clumsy giant, but the A.S.P is in reality fairly human-like in its movements and only double the size of a man. You have to remember that your character was forced to reveal itself to avoid the last attack, so Higan was able to start moving the arm from that point onwards. The hand is literally reaching the Pater at the same time as its rock, so unless you've sped up the action by reducing the power of the blow it doesn't work. 

Also, the positioning for your character is exceedingly awkward to once again avoid being crushed against the wall. Though I concede that Shash has the ability to squeeze through narrow spaces, I wasn't under the impression that meant he had full size manipulation powers. He seems to have made himself perhaps half the length you stated (considering there was no mention that it could actually shrink its length, only that it can slither through tight spaces.) in order to carry out these actions on the Mech. In actuality tail included Shash is longer than the Mech is tall. 

If Shash's entire body was away from being crushed by the wall and it was in position to hit the optic system it would have had to reduce its overall body size (disregarding the tail) by at least half, maybe even three quarters.