It seems like you’re spending a significant amount of time and money trying to get the measured temperature to match some value, but from your posts I can’t tell if you’ve tried welding any scraps of fabric to see if there’s actually a problem there that needs solving.
If so, carry on – I just don’t want to leave other readers with the impression that they need to be measuring temperatures and fiddling with transformers and such when the vast majority of people can simply plug in their irons and find the correct temperature by welding scraps of fabric together and then pulling them apart, as shown in the instructions.