Hi,
its more conventional to change the battery/pwr supply & your resistor (battery + pole on Collector & -pole & resistorcommen=reference point, other resistor contact on Emitter-as another measuring point or pulse out), & referencing to the Emitter (as you maked), but important is to measure only on the resistor!
Because your system is floating; you can make it_measure only over the resistor_ not from emitter...
The above descripted connection makes no phase reversing or inverting to optocouplers inp(unknowed) input.
Otherwise if you need an inverted signal_ no problem: connect battery -pole to Emiter, these point is reference potential/output GND, & connect resistor to collector and the other resistor pole to battery plus pole: In these circuit is pulse out from collector to take, even GND/or reference potential at the Emitter.
Dont worry, you have an output transistor, of course, in the optocoupler in the "Power Meter Unit", but what you are writing-I didnt get it 100% .
K.