When you play the T i m roll (forward roll) I and m move in the same direction (sympathetic).
T plays i and m move out together.
i plays pulling m to the string, m plays.
i and m move in the same direction.
Most people incorrectly alternate i and m. (They play i then move m out (alternation).
m should move out with i when p is playing.
The principle of uniform joint movement: The tip joint, middle joint and bottom joint (right hand index finger) should be moving in the same direction (flexion) when playing. There is a tendancy to lift the bottom joint when flexing the tip joint to play a string (opposed movement).
These are two problem areas. I can give more details if interested.