Correcting My Freestyle: Going from an S-Pull to an I-Pull

Let's keep it simple. Rt hand enters Rt hands thumb follows the right hand side of the black line on the bottom until you get to the finish. Repeat with the Lt hand on the left hand side of the line on the bottom. No stupid drills needed. This is very helpful for me. But, when you say "Rt hand thum follows right hand side of black line..." is the hand FLAT during this, or is the hand vertical so that the thumb is the first finger following the line? Not sure if my question is clear--does that make sense?

Let's keep it simple. Rt hand enters Rt hands thumb follows the right hand side of the black line on the bottom until you get to the finish. Repeat with the Lt hand on the left hand side of the line on the bottom. No stupid drills needed. This is very helpful for me. But, when you say "Rt hand thum follows right hand side of black line..." is the hand FLAT during this, or is the hand vertical so that the thumb is the first finger following the line? Not sure if my question is clear--does that make sense?