I find it hard to believe that most people feel comfortable with 25 – 28.3 °C, how to come up with this numbers? Based on the link above? It seems rather hot. Also it would depend what the outdoor temperature is. But different people have different preferences https://comfort.cbe.berkeley.edu/ (comfort calculator)

ahh 19/20/21 based off the chart - that is more reasonable. I probably would not have bothered with the conversion as humidity indoors is fairly consistent and it appears the index is more designed for summer / higher temperatures rather than winter clothing indoors etc.