You are correct in your assumption the split in the skin is one "ring" or scale length closer the body. For me this is all easiest to see and explain when looking at the tail from underneath.
The first 4 scale lengths at the end of the tail are hard and brittle (and much narrower and not in proportion when compared to the next one up. The next scale length up towards the body (#5) is a bit more narrow on the end that is closer to the hard brittle part, while the other end is more normal looking when considering its proportional correctness in relation to the surrounding areas. The split in the skin is between this fifth scale and next scale length towards the body (#6).
We have a 3pm visit today and have been putting a bit of ointment on the tail tip in the meantime.
We trust our vet and will let her do what she thinks is best, but out of curiosity would it not be better for the ig to naturally drop the end without assistance from myself (not happening) or the vet?