Just one of the players here so not sure if it's a bug but you can change who will be how tall with the cheats or before starting a game you can go to world generation options where you can choose a lot of stuff (___modifiers, multipliers, __ distribution,....). What of them is Height modifier where you can choose what height you want most of the npc to have. To be honest I'm not sure if I'm right or not. Sorry if it's wrong