Thank you for the note, however, it works exactly as it was designed - there is/was no requirement for it to work exactly like default vbulletin - I won't be changing it.
If you set the factor to 0.5 then it will almost be the same, the two exceptions being (as you have found) if your positive rep power is 1, then your negative rep will be 0 (not -1). The other exception is already mentioned in the notes (fixed Admin rep power). I will add another note to point out this small difference.