When I use a crossover movement, I find that pick blocking this type of move can slow you down. If the pick has to go back to the strings and block at the same time it's crossing over then there is a conflict. To help eliminate this problem I developed thumb blocking techniques.
To fully utilize the thumb block we must first look at right and left hand tracking. This simply put is where the right hand goes, so does the bar.
The pictures above show how the right and left hand must work together. As the right hand moves towards the lower strings the bar follows right along. This can be practiced without even picking the strings. Simply move your right hand and get the bar to follow wherever it goes.
When you get the tracking movement mastered then you are ready
to work on your thumb block. The pictures below show the thumb in
the ready position and then shows you how it moves down to block