Tartine Bread. Want more open crumb.

Hi, I was wondering if you could help me with a problem I'm having with my crumb. I can not get the open holey crumb I am looking for.

I use 100% hydration Rye starter. My levain is 100% hydration 200g AP  175g Whole Wheat 25g Rye 200g water

it is nice and vigorous when I use it usually 9-12 hours later.

i then mix the dough, autolyse 60 mins add the rest of the salt and water.

previously I have done vigorous turns trying to develop more structure in my dough. I was not yet used to the higher hydration doughs and had some problems with poor gluten development. 

Recently I have mixed just to incorporate together the dough, and then again the salt. And for a 4 hour bulk fermentation didn't touch the dough at all the last 2 hours. 

I probably could have let it go another couple of hours. It was,quite cold. Nod not a ton of bubbles had developed

i handled the dough, which was still a bit sticky less then normal, not even flipping it just circling the dough into a round mass with my bench scrapper from the sides and bottom.

i bench rested 20 mins and then shaped my dough. There weren't A ton of big bubbles and I took care not to knock any out. I shaped it put it in my banneton and stuck it in the fridge where it got a nice rice baked from cold in a Dutch oven. I use a spray bottle to steam and it works really well. I always get a great crust but a poor open crumb. The bread tastes really good and has lots of small bubbles in it but not the big ones I am really looking for.

i use a small oval Dutch oven, and get great oven spring. 

My starter is vigorous fed rye 2x a day everyday but also has small bubbles.

i also just noticed my Banneton is for 1.5 pounds and I've been putting about 800grams of dough in it. 

Any and all suggestions please!