A good example of this in the game is the Titan Quest. You can see the movement of experience even when killing weak mobs. And also the movement of experience in time. I know that this is only a psychological effect, but it's easier for me to play.
I suggest create page, when you can choose location and percent of drop and get item list who drop in this location with low/hight choosed chance. Its 1 SQL request, i don't now DB shema, but with my variables names it will look like this: SELECT it.* FROM items_table it JOIN monster_table mo ON mo.items_drop_id = it.item_id JOIN location_table lt ON lt.monster_spawns_id = mo.monster_id WHERE lt.location_id = 'moc1' AND it.drop_chanse < 50