I am not a Bell rep so the information below is worth what you paid for it.
1. The check at idle checks the timing between the two systems pilot valves so that you know that one hydraulic system is not fighting the other. As you know the servo is actually two servos mounted together and redundant. If the timing or pilot valve centering is not the same, when you turn off one system the control will jump the distance needed to recenter the pilot valve.
2. For the check at 100% you needn't be concerned about the controls jumping as you have already confirmed this at idle. The real check here is to ensure that you can't turn off both hydraulic systems at the same time. Bell wants to make sure that you can't turn off both hydraulic systems by mistake. This has happened in the past via improper maintenance or other items installed by people that supply the necessary ground in order to turn the system off. When you turn off the hydraulic system you are actually powering the solenoid valve to the off position. Hyd #1 valve actually supplies the ground for the #2 valve and #2 supplies #1's ground. That way if one system is already off, then the other system can't be turned off unless the original system's switch is positioned back into the on postion. By using power to turn the system off, acts as a fail safe, so that if you loose all electrical power you won't loose hydralulics. As you know the 412 can't fly without the red stuff flowing through its tubes...