Hi Suki,
there are different 'movement types': One is rotating the hip axis against the shoulder axis, the other is not doing that.

In fact, responsible for the hardness of a spike are:
- Arm extension out of the elbow joint - 46%
- Rotation of the arm out of the shoulder joint - 23%
- Rotating thorax/shoulder (picture right) OR shifting thorax/shoulder (picture left)- 15%
- Movement of body's balancepoint (in space) - 8%
To get the optimal spiking hardness out of your player you have to first recognize his movement type and then work WITH it, not against.
You cannot change those movement preferences.
Greets,
Baumi