Since 2015 Watts has played the vast, vast majority of his snaps at Edge. He will sometimes move inside on 1st down in a 2 man front and play LDE.
Even before 2015 the vast majority of his snaps were at Edge. 82% to be precise. And it's risen since then.
Here's where he played in 2020.
702 snaps as the left edge defender, 134 as the right edge defender, 90 snaps at left end in a 3 man front with an OLB outside him, 32 snaps at right end with an OLB outside him, and 28 snaps combined as a defensive tackle/nose tackle.
That's 84% on the Edge.
There's no way that the Cards are paying Watt $14m per with a 10 sack bonus to play inside. He's going to play 80%+ of his snaps on the Edge opposite CJ and all that would be left for Reddick is scraps.