There are a lot of factors that can affect readings. Steam engine is more detailed than it even appears to be, but even it is not capable of perfect accuracy.
Claptons, I've noticed, tend to have shorts that jump from section to section before everything is properly oxidized. Simply working out the shorts can change your resistance significantly. Very rarely will a fresh clapton read as it does initially. Sometimes, it gets a little worse after the first few pulses, when the pathways between semi-oxidized patches form a mainline for current to jump through.
I will say that I've had some builds that sat literally .004 away from the projected resistance right off of the bat and stayed there. It tends to happen most often with my dual and triple parallel builds. Maybe it has something to do with the straightening of the wire. Or maybe it's because the two or three leads that are touching are each carrying their own current at similar resistances. No clue, there.
Another thing that can happen is a connection short. A coil can ohm lower than it should if the current is being split at the connection. Or perhaps it's more accurate to call it uneven contact across the surface of the wire in the post. When this happens, you will see numbers that seem mathematically impossible for a coil that's firing evenly. I've seen a coil's resistance be cut in half after pulsing only to double back up to where it should be with a quarter-turn of a screw.
Sometimes, you have to tighten it down a little more or back it out and bring it back down to get it to read and fire enough for you to oxidize. As you work the kinks out and continue slightly tamping the connection down while the leads are still hot, the resistance should get back up to where it should be. You just have to be very gradual to avoid clipping anything. It can take some time.
I've noticed that I have this problem quite a lot with the Mutation X v4 that you're building on. It performs great, but it has connection problems. I hate building on the thing, myself. The posts themselves are bored-out too deep (I'm talking about from the holes the screws go into,) the tolerances for the threading don't quite match the screws, and the post holes are as thin as they are jagged. They have a tendency to essentially require you to pull too much wire in to get a secure grip and really mess up the wire inside the post holes in the process. Sometimes, it takes some doing to get a coil to properly settle in.
I'm sure that this all sounds like nonsense, but I'm telling you, I've seen it happen!
