I have no idea what is going on with my two upgraded units then. I have now taken the "upgraded" units back to v1.4 and both no fire the 0.063 and the 0.8 units fine....they just won't fire on 2.21 no matter what I do. If it was only one device with 2.21 that wouldn't fire the lower ohms I'd think it was a hardware problem. When two devices with 2.21 won't fire lower ohms....but do fire lower ohms when I go back to v 1.4??? don't know what to say....I tried my Subtank Mini and that calibrated and worked just fine at .075 so I then tried my Delta II which calibrated at .055 and is working just fine also. I am running the yet to be released v2.21 firmware.
So I am not sure what is going with your setup but it is not a limitation of the v2.21 firmware as I have just confirmed with a .055 build which is close to the bottom end of the Yihi SXM specifications.
except maybe there is more than one 2.21 version out there.....? Any chance you could send me the upgrade file you used? PM me if you are willing. I'd appreciate it.
Duane