In my circuit there is 300k ohms of "isolation". You are not really on the power line.
Optocouplers are not linear or temperature stable.
MCT271M has a gain of 45% min to 90% max at 10mA and 10V.
MCT2E has a min of 20% and a max of ? at 10mA and 10V.
View attachment 85353
Here is a graph of CTR (some thing like gain) of a part.
A gain of "1" at 3.5 and 10mA.
Gain of 1.1 at 6mA
Gain of .65 at 20mA and 1mA
You can see the gain is very non linear below 2mA.
Use the part from 4 to 9mA.
View attachment 85354
Here is the CTR verses temperature.
At 10mA the gain changes 6% from 0C to 25C.
Spice does not model this very well. You will have to try this.