Open up the Radeon Adrenalin program, go to the Games tab, Global Settings, Global Wattman. Scroll down to the fan speed graph and change "Automatic to Manual" and adjust the graph to where the fans speed is better at 70-80C. I changed mine after I was peaking at like 94C and after adjusting fan graph it did not go above 75C. Just change same fan speed at 90C default to be the temp at 70C manual and it should work great!
Correct that is how they do it. But you can change at what temp the fan is a certain speed so effectively it is the same. I too liked it better when it was split.
My RX 580 runs really hot too. I can share how I set my curve for it if that helps? My pic is from a few driver versions back but works the same way, just looks a little different.
Sapphire has a cooling/fan application that is installed along with the drivers. This is not available on every card...and I can't find the info on this particular card. Check to see if you have any Sapphire program that has to do with cooling/fans. Something like cool n quite.