I was experiencing quite some edge curling during prints (PLA, overhangs), so I tried printing this thing with various settings. with try 2, I was able to print without any upward curling, and got pretty nice results up to 30 degrees. 25 degrees is also acceptable. what helped for me:
-layer height 0.2 as usual
-extrude perimeters with width 0.6 instead of the nozzle size 0.4 (just tell cura the nozzle is 0.6!)
-shell thickness went from 0.8 to 1.2
-increase temperature to 210 degrees
-importantly, lower extrusion speed to 20 mm/s (all this based on nopheads die swell/filament stretching theory!)
-just before these tests, I added a second 40mm fan to my extruder, which probably also helped.
not sure what helped the most, but I'm happy with these settings!
the first variation I tried was based on nophead's theory, and I was actually unable to find better settings. listen to this man!
-think3dprint3d kossel mini v1, plus extra 40mm fan attached to extruder, without any fan duct
-colorfabb pla/pha (sky blue)