In the exotic technology section for astrogation checks for hop drives, it says this:
"In addition to making hops possible, Hop Control software reduces the distance in parsecs – for purposes of calculating DM for Astrogation checks – by 10 rounding up (minimum one)."
I suspect that should be divided by 10 rather than reduced by 10 or anything more than hop 1 will be virtually impossible.
Edit: Looking at the Singularity entry for hop drives, it says this, so the wording in High Guard should be updated to match.
"In addition, the hop governor reduces the difficulty of all astrogation DMs to one level per hop; therefore, any hop of 1–10 parsecs only incurs DM-1 on the astrogation check. Likewise, while the technology does not exist for a hop-2 (it will not until a TL18 version of the drive can be built), if there were a hop-2 drive, making a hop of 11–20 parsecs would only incur DM-2 on the astrogation check."