You should try not to sit too much time in the same position if you have piriformis pain as it increases while sitting.
I do not know a reason but it is tested on my own “butt”.
What I do:
● it is hard to get a habit from this but I always change position after 15 mins
● i alternate sitting with walking for 2-3 mins, might not be enough but at least i keep myself away from the chair for a short period
● while driving for long, take breaks each hour and get out of the car for a short walk
It’s not the ideal path but at least following the rule of not sitting too much in the same position!