tl;dr - sorry in advance if this has been said.
When sitting, the bass rests on your leg and that determines the position of the neck related to your body.
When standing, the bass hangs from the strap and that determines the position of the neck relative to your body.
It isn't about whether or not your rest your arm on the instrument. It is all about the strap going over your shoulder and where it attaches to the bass. If you want standing and sitting to put the bass in the same position, you'll need a different bass body shape that has a leg cutout back by the bridge.
When sitting, the bass rests on your leg and that determines the position of the neck related to your body.
When standing, the bass hangs from the strap and that determines the position of the neck relative to your body.
It isn't about whether or not your rest your arm on the instrument. It is all about the strap going over your shoulder and where it attaches to the bass. If you want standing and sitting to put the bass in the same position, you'll need a different bass body shape that has a leg cutout back by the bridge.




