Crumb question

Today I attempted to bake Reinhart's pain au levain from his "Artisan breads every day" beginning yesterday with the levain (sourdough starter from a friend), mixing, blending, adding flour until the dough was tacky, four sets of folds and then into the fridge overnight.  During that time, the dough tripled in size.  Using the whole ~ 3 lb amount in an attempt to make a miche, I let it warm two hours this morning, then did a four fold, let it  rest, then tucked things into a boule and let the dough to proof on parchment in a plastic strainer/banneton for two more hours.  The surface was sprayed with olive oil at the beginning and covered during this time of proofing.  Touch test and amount of rise suggested readiness at two hours. The top was scored and corn mealed and then into the preheated Dutch oven at 450 F it went for 30 minutes.  When I lifted the lid, the top of the loaf was slightly above the edge of my 5 quart Dutch oven!  Then another 25 minutes at 425 F and the temperature had reached 205 F inside the loaf.  The final loaf weight was ~ 2 1/2 lb with a ~ 20% weight loss.

 This is easily the most spring that I've ever had with any bread recipe.  I estimate that the dough doubled in size before the crust hardening arrested further movement.  So I'm quite happy.  But then I saw that the bottom and top surfaces had a 3/8-1/2" somewhat compressed layer - but not the sides.  I'm guessing that the crust hardened before the bread could completely expand.  Would this mean that the bread was under-proofed? I'm not trying to be too picky about this, just trying to understand...

    aloha,

Dave Hurd, Hilo, Hawaii