Could it just be that the 0.8 is before you cut the length down by fitting it?
The effective resistive length is between the post clamps/screws.
If you lose 20% length that would take it from 0.8 to 0.6.
Hmm that's interesting, I guess it could be. When I see videos of people building coils they don't seem to have this happen though, like if they use a 1 ohm coil it shows 1ohm after they cut and prep it. Maybe it's just the ones I have (all 3 brands of them).