When the mini came out, I posted threads on the forum regarding the consistency of the heads. On a ProVari, these 1.8 ohm coils actually read out in a range from 1.8-2.1ohms within the first install. That much variation is just in one five pack of coils. So honestly I wouldn't be worried, just keep on vaping that coil 'til you burn it out, or gunk it up beyond belief.
After awhile, gunk will start to build up on the coil itself. With clearos there's nothing to be done about this because you can't dry burn the coils. One of my ProVaris with a nautilus mini is on permanent loan to a friend of mine. He's very new to vaping, and doesn't yet know the requirements of vaping. Anyway, he said the PV wasn't hitting right, he's been using one coil continuously for about two or three weeks now. I checked the resistance of the coil (1.8-2.1 when new, mind you) and it was a whopping 3.1ohms! I cranked the mod up to 6.0volts, and got a plasticy taste. Coil gunked beyond belief.