Playing chords

Can someone explain to me why I can play chords cleaner while I'm standing up than sitting down and also there's less stress on my fretting hand...thanks for your input

You probably hold your guitar in a better position which allows less restrictions on your tendons.

Try taking careful note of how you hold the guitar when sitting or standing. For a guess I would say you either tilt the head of the guitar downward or away from you when sitting and hold it higher and nearer to your body when standing.

Thx for the advice