Originally Posted by bkpr
Do you mean pointing your toes towards the net more? Currently my left/front foot is almost parallel to the baseline, pointing a little into the net, but not much. I understand being more 'open' is also moving your back foot out from behind your body, and for a righty, a little to the right. Is this what you mean/do?
Exactly, starting out facing more towards the net.
Before I did what you/I described above, there wasn't much freedom for the shoulder/upper body to uncoil in a linear way (to flatten out more down the middle), so all I would get is a medium-rate slice that would split the service line when I would try to go down the T. What you did by angling off even more (even more parallel to baseline) made it impossible to hit the T by simply following through in that direction.