Go as wide as possible without the rim tape going up on the sidewalls.
I actually ran into the same dilema when i got new wheels earlier this year (Xero XR1). They had the same narrower channel in the middle so i started out putting the 10mm rim tape on which fit perfectly in the center channel but bearly covered the spoke holes. I rode maybe 50-60 miles without issue but it still nagged me in the back of my mind. So i picked up some 17mm rim tape (velox of course) and when i pulled the tires off to check, the 10mm tape had slipped a tad in afew places which exposed the edge of afew spoke holes. Needless to say, i put on the 17mm tape and haven't looked back.