Well the big no no is more tail than nose. But I would hope that's fairly obvious.
If it's a true twin it's designed to flex equally so you want the stance equal for sure.
If it's a directional twin meaning twin flex but with a set back you can either go with the set back or you can twin it based off the twin aspect which is usually contact point to contact point.
If it's straight directional you want the stance to optimally be based off the set back and be equal, but you can go with more setback based on conditions/riding preference.
At the end of the day any experienced rider should know their stance width/angles and what works for them. I've seen some fucked up stances in my day like the chick that was 5'5 and had a stance width of 29 inches with 45 negative 45 degree angles.