Interesting - the way I've been doing the palm switch is slightly different too..
Whilst the coin does drop straight down, reading Dan's description above made me realise that I might not be doing it as described by Roth.
I display the coin between thumb and index finger.
Turn the wrist down and drop the coin straight onto pinky and third finger, almost at a finger tip rest position, not quite a high finger palm.
(At this point I have two coins at the fingertips, not touching)
As I make a fist the coin I actually use the middle (second) finger to push the first coin into classic palm.
Then I rotate the wrist to a vertical position, pushing up the switched coin with my thumb to the starting position.
From the spec's point of view, coin is visible at finger tips, the coin moves down, in an arc, then into a fist and then reappears in at the fingertips when the fist is opened.
Anyway - it is what works for me.
[ Not used to describing sleights, so apologies if anything is unclear, and happy to clarify any descriptions]