That is weird.
The OTO showed you "maybe .5ppm FC". If FC is above 5ppm, that test is very yellow, and if it was equal to 30 drops R-0871 it would actually be more orange than yellow.
If you use your CYA of maybe 20, then add enough chlorine to get to 5ppm FC (which it appears you need according to the OTO) and then redo the FAS/DPD powder test. I can't imagine why it would behave that way, but this should get you better results. If it still doesn't work, let us know.
The OTO showed you "maybe .5ppm FC". If FC is above 5ppm, that test is very yellow, and if it was equal to 30 drops R-0871 it would actually be more orange than yellow.
If you use your CYA of maybe 20, then add enough chlorine to get to 5ppm FC (which it appears you need according to the OTO) and then redo the FAS/DPD powder test. I can't imagine why it would behave that way, but this should get you better results. If it still doesn't work, let us know.