You need a Transistor array in RL since they have to match as perfectly to each other than possible.
By regulating the current on the transistor with the base connected to its collector, all other transistors try to let the same current flowing.
The trick is that for every current through the Emitter, a specific base voltage is created which when tied to the other bases causes the same emitter current if the load allows this. To create this base voltage, the collector of the "sender" needs to be connected to the base. Try the switch.
