"Incorrect" XP for NPC
Why am I not getting the correct XP on custom NPCs?
As with most awkward situations this involves two different plugins not communicating with each other correctly.
The plugin that handles XP is not the same plugin that lets us run custom NPCs. And neither has native support for allowing custom XP values per NPC profile (profiles are groups of NPCs such as "Abandoned Prison" or "Project Riese" each is considered a profile).
The XP is actually getting awarded correctly via that API call but the popup just displays the default base value. You are actually getting the default base value (for killing a scientist, which is what our custom NPCs really are) and then a bonus XP on top of that via the API for killing a custom NPC. That bonus is the part not being included in the pop-up. There is no fix for this at the moment.