>>323535153
The viewball location should not have any influence of the FBT, given it's at the same height.
Making the arms longer pushes the hip tracker down towards your crotch(to avoid the stunted leg avatar look).
Making legs shorter is better for fbt if you can't make the arms longer.
If you can post of you calibrating into the avatar, avatar in T-pose with the white tracker balls visible, that might help.
Else experiment yourself with what I wrote.