I studied preseason YPA a decade ago and found it to be worthless for early season wagering. Very low correlation, not nearly as reliable as simply using the prior season numbers. Tannehill has already established a level and it's far beyond 5.6. The concern, obviously, is if he doesn't build from there.
With 16 rushes at halftime he needs to be well into the 7s if it's a regular season game.
BTW, I was actually very happy when Matt Moore threw that pick six. Those influence plays need to go DOWNFIELD, as I emphasized after the Falcons game. Too many new coordinators think they can get away with perimeter garbage in the NFL. This isn't the Mountain West where every team is determined to allow 8 YPA no matter what you throw at them.
Get the sideways garbage out of the system now. I was also pleased when we tried a cheap slip route on 3rd and 1 with Tannehill in the game and Dallas surprisingly blew it up. Our short yardage formations and play choices have been perhaps the most disturbing aspect of preseason, far beyond Tannehill's YPA.