Why larger air holes on ends but less in center?

I always notice that my boules have end pieces that are airy and filled with pockets whereas in the center, the crumb is a bit more dense and there are less holes. The flavor/texture and rise is always very good.

Recipe:

Starter fed at 1:3:3, let rise for 7 hours, tripled in size. The starter is well-established and from a friend who claimed it is decades old.

Dough:

330 g water 120 g starter 500 g King Arthur organic bread flour 2 tsp salt

1 hour of autolysation, 3 stretch and folds 30 mins apart, then BR for 3 hours, in fridge to slow rise, took out next morning and let BR in a 75 degree kitchen for 4 more hours, then put back in fridge for one hour before baking. Baked in preheated dutch oven at 500 degrees for 25 mins & then at 450 for 25 mins. Internal temp was 205 degrees when I removed it