Great improvement in oven spring - Sharing my experience

Hey TFL community,

How's it going? I hope all is well with you all in this wierd chaotic time of COVID.

I baked a batch of 2 sourdough loaves today, and had some great improvements based on some tweaking I did in my technique and fermentation time that I'd like to share with you guys. As you know, from time to time, I'd document my sourdough baking experiences here.

A couple of weeks back, I had a loaf that looked like this:

While the loaves were good, they did not have oven spring I wanted. The technique and percentage I utilized for these loaves are as follows:

800gr strong bakers flour

200gr wholemeal plain flour

200gr white rye starter

750gr water

20gr salt

!) I initially mixed the starter, 700gr of water water and flours together and left them to autolyse for  20 mins

2) After autolysing, I added the salt and the extra 50gr of water and did my first folds. 

3) Bulk fermented for 4 hours, doing 4 turns of folding within the first 2 hours

4) Bench rested for 20 mins and pre-shaped loaves

5) Shaped loaves and put into bannetons

6) Proofed for 3 hours at room temp, but the last half hour proofed in freezer for easier scoring

7) Baked at 250 degrees in dutch oven, lid on for 20 mins and lid off for 25 mins. 

Today, I baked up this loaf, changing my technique and fermentation time, and believe I've had great success.

The changes I made and my steps are:

!) After adding my flours, starter and 700gr of water, I slapped and folded the dough for 7-8 minutes to produce a very supple and airy dough

2) I then autolyzed the dough for 20 mins, then added the salt and extra 50 gr of water. I did some folds in the bowl first then put the dough on the counter and stretched an fold the dough about 8 times, making it into a loose ball and putting it back into the bowl

3) I extended my bulk fermentation from 4 hours to 5 hours. My internal room temp was fluctuating between 17 degrees celcius and 19 degrees celcius. Within the first 2.5 hours, I stretched and folded the dough 3 turns.

4) I bench rested the dough for 20 mins and pre-shaped the dough, but less tighter then last time, being careful not to degass it. After preshaping, I shaped the dough into batards, but this time I utilized Chad Robertson's shaping technique from his tartine book. 

5) I extended final proofing from 3 hours to 4 hours. In the the hour mark, the dough looked quite on-point. In the final hour, to not overproof the loaf, I popped it into the fridge which according to my IR thermometer was about 10 degrees on the first rack.

6) Baked my loaf in the dutch oven lid on for 10 mins and lid off for 20 mins. The caramelization and crust seems to have been much better than my other loaves because of my extended bulk fermentation. 

What do you guys think? I haven't been able to cut into the loaf yet to see the crumb as the loaf is still quite warm.

Best Regards