Watching the Martin Miller vid over and over again…
He most of time hits the strings with just the very tip of the pick.
When you watch the Arpeggio Crosspicking vid in slow mo you can see this very well. Somtimes it almost looks that he does not hit the D and G string at all, so little of the pick is used.
I see this also happening Michael Angelo Batio, although he has a different techinique overall. But i think this is a big factor in achieving this very accurate fast alternate picking.
You then almost need no outward to get over a string.