Bulk Fermentation Experiment

I am a crumb enthusiast and have not been able to bake my ideal crumb for a long time. Therefore, I have decided to conduct an experiment with different lengths of bulk fermentation time (7 hours, 7 hours 40 mins, 8 hours 20 mins and 9 hours).
The result was phenomenal! My dough temperature was between 72-76°F (final dough temperature 75°F).
The dough rises to 1.5 times its original size at 7 hours, almost 2 times at 7 hours 40 mins, and approximately 2.5 times at 8 hours 20 mins. It reaches 3 times its original size at 9 hours. As expected, the pH of the dough decreases with longer bulk fermentation.
I honestly thought I would bake 1 or 2 frisbees, but all 4 loafs turned out to have good oven spring. 8 hours 20 mins had the best oven spring, follow by the 7 hours 40mins loaf, and the least oven spring ones are 7 hours and 9 hours loafs.
I think the 7 hours loaf is slightly underproofed due to the presence of a slightly dense crumb. The crumb opens a bit more in the 7 hours 40 mins loaf. The 8 hours 20 mins loaf seems to be the most properly proofed loaf. The 9 hours loaf seems slightly over-proofed as the crumb begins to close down a bit.
The scoring expansion wideness seems irrelevant with bulk fermentation. Yet, I am still clueless in regard to how I used to bake wild open crumb half a year ago. But, I can now confirm that the perfect timing to end bulk fermentation at 72-76°F is when the dough is more than doubled in size (over 100% percentage rise).

My recipe :

• Levain 12 hours 1:6:6, pH 4.01
• Autolyse 9 hours in the fridge, 100% Bobs red mill artisan bread flour, 80% hydration
• 20% Leivain
• 2% salt
• 1 fold
• 1 lamination
• 3 coil folds separated by 45 min
• Shaping
• 7 hours (dough final pH 4.65), 7 hour 40 mins (pH 4.57), 8 hours 20 mins (pH 4.50), 9 hours (pH 4.41) bulk fermentation at 72-76F. (dough final temp 75F)
• Retard at 35F, between 13 hours 20 min ~ 15 hours