I’m playing in ANY world, and no matter what I do my arms are short in any single avatar I choose. Infact, In one of my avatars, my arms reach max length when it reaches my mid upper arm, I can play but it’s still very annoying
In the settings menu you can change the scaling mechanism to be based on arms or legs. Try using the arm one and it may be more realistic and based on your actual arm length.
I have a doubt if this is only for full body or not. But try to find that feature. Hope it helps.