I am not sure fully understand your meaning ,I try to explain this more clearly .
Fisrt ,Z safe sensor have 2 seperate parts ,one is emmiter ,the other is receiver .
There's one hole on each spindle ,if all spindle on a same height ,then the 7 holes will be in a straight line .It looks like a long pipe in side view .
The Z safe sensor is in located in upmost position ( Not exactly correct ,but almost ) .Emmiter send one light beam in horizontal , If all 7 spindles are in a upmost position ,then light beam will go though all 7 spindles reached the receiver .That is Z safe status ,Also mean all spindles are in upper position .