@Mark Regarding this:
"I think the OP is assuming TO REDU is the same as TO FLEX, when it is not in this case."
The FCOM says:
The "REDU values are just particular FLEX values".
The mode TO REDU on the TRP carries out the calculation I posted multiple FCOM references to.
When you push the TO REDU button, it will set a default T FLEX, this temperature is called T REDU.
You can actually calculate the values in the N1 REDU table using the method I provided. The reason for this is simply that N1 REDU is the same as N1 FLEX, it's just been decided that a particular T FLEX will be called T REDU.
If your TRP implementation isn't carrying out the calculation I provided from the FCOM, then it's not doing what the real aircraft does.
How can I be so sure about this?
I did the calculation using real data from 3 videos and my calculations matched the N1 set by the TRP for the particular temperature setting in the videos and pressure altitude (±0.1% N1 precision is acceptable).
If I was wrong about all of this, then the calculations should return non-matching values.
When I do the exact same scenarios in the JF RJ, the values output by the TRP doesn't match at all.