It’s because the avatar has longer legs proportionaly.
Stand in front of a mirror and lower your hight in the settings untill your legs are straight. Now note the difference. [Note that your view height will now be too high]
If you had to drop the hight 6 inches to stand, take note of that
Jump into another avatar. Now add the 6 inches or whatever the difference above was.
With your height set higher fist, try on the avatar again, now set the height to your real height.
You will have the foot balls in your shins but this is not a problem.