The float is the control element for the valve - they would not go to the bother of fitting a float if it had no function as you seem to suggest.
The float rises on a pivoting arm and applies movement via a nylon adjusting screw to the inlet valve - sometimes the "rubber" in the valve has perished but more usually it just needs adjusting and the lock nut tightening on the screw to maintain the setting.
The ball/float does not attach to the syphon/flush unit as you state but to the water inlet and control valve assembly.
Judging from the text in your question you may not be interpreting the function of the two main components correctly - the flush syphon attaches to the operating handle - the float attaches to the water inlet valve.
Peccavi
January 2010