That's not entirely accurate. You can set your irl height in the settings. I can use any avatar from extremely small or tall and it doesn't matter as the game scales everything correctly. You can also just scale it in settings however you please if the avatar still doesn't fit properly. But for avatars where you have to change these settings massively they just don't have the proper proportions to begin with. Like i know some Anime avatars have really short arms and i have to max out the height settings ingame so it kinda fits. But with all of my avatars it works perfectly fine regardless if i upload a few centimeters big version or multiple meters big.