Now, I know that there are a lot of threads about this, but that didn´t really help a lot. Basically, Viconia has that innate -2 to Reputation which most probably know, but I seem to have a problem keeping evil characters in my party at a max Reputation, even though they should remain in a 18 Reputation party.
Is the loyalty of evil characters based on the 18 Reputation, or is it based on the base Reputation before you get the -2 modifier from Viconia? Korgan and so on tend to bolt, hell, even Viconia leaves.
Evil people leave at rep. 18. However, say you have rep 20, then ask an evil one to join, they'll stay until you get a rep boost (even if your at the max).
"Hurrah for anarchy! This is the happiest moment of my life." George Engel, just before he got hanged
Viconia doesn't have "an innate -2 to Reputation", your party just gets -2 to reputation when she joins and +2 when she leaves. In SoA evil party members leave at 19-20 reputation, no matter if Viconia is in your party or not.