To elaborate, our XP is all derived out of a relatively small table. We establish tiers of quests (by character level) and allocate a total amount of XP to be spread among all quests marked for that level. In turn, each quest is marked with a given level and as major, standard, or minor. The major/standard/minor classifications determine relative proportion of XP share that the quest gets when all quests are taken into account. So if 28 quests are marked as level 4 and level 4 quests only have 1000xp allocated for them, the per-quest reward is really tiny. We mostly just adjust the allocated XP in each tier and what quests are classified as, level-wise. To accommodate additional sources of XP, we start by determining those fixed-pool allocations and subtract them from the total quest XP. The exploration-related XP is a) not large and b) easy to quantify. The bestiary-related XP is also relatively easy to quantify because we associate total XP per bestiary entry, of which there are a fixed amount. We still have to tune after that basic estimation, but it's not a hard or time-consuming process overall.
We currently track within 1 level of our expected targets for XP acquired over the course of the game, so I'm not too worried about it.
