Critique my Tartine loaf

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Hello,

My first attempt at Trevor J's tartine method.  Autolyse for 3 hrs, then add salt, starter, raubaud(?) mix until smooth (10 min, rest 5 min, mix 5 more).  S+F every 30 min for 2 hrs, then every hour for 5 hours (7 hour ferment), preshape, then shape with 'stitching' method.  Bake in combo cooker for 500 covered for 15 min, 450 uncovered for 15 min.  

I am looking for a MUCH more open crumb, so if anyone has any tips, I would be eternally grateful.  Thanks!