Smaller loaves vs bigger loaves - weak oven spring :(

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Hi,

I've recently started a journey with my starter, it's now 2 weeks old and capable of producing loaves with oven spring that is completely satisfactory for me...as long as the loaf is bigger than 1kg bread. 

Anytime I try to make a smaller bread, I end up with - tasty as it is - low oven spring (worth mentioning that there is some spring, but very weak and very slow in the oven (I've observed the loaves in panic a couple of times now).

Example recipe that "failed" to produce a good oven spring:

405 g wheat bread flour

45 g whole wheat flour

8 g salt

1 baked, smashed garlic

295 g water

levain: 15 g liquid starter, 70 g flour, 85 g water

 

The method I follow is a combination of J. Hamelman's advice and videos by Joshua Weissman and Pro Home Cooks.

-> I set the levain first and use it when I see it doubles/triples and its rise slows down, but is still in its peak (it takes around 6-7 hours). 

-> 2 hours before using the levain I combine flour and water only for the autolyse

-> Then I combine levain and water/flour mixture together, perform a series of slap n' folds and let rest for 30 minutes

-> I add salt and garlic and perform another series of slap n' folds until I see the texture change

-> around 2.5 h bulk ferment, it doubles nicely (including two folds)

-> preshaping, 20 minutes bench rest

-> final shaping and proofing (I've tried 1-1.5 outside the fridge, to my mind poke test showed it overproofed; but I've also tried 7-8 hours in the fridge and it also seemed overproofed, the dent does hardly go back)

The result is on the flattish side, it has some rise like I said, but very very poor; the crumb was generally OK with those loaves, maybe a bit dense, but definitely not a brick, some nice air pockets were present.

Is it possible that the dough is working so quick in the proofing stage that it gets overproofed everytime? Is it because of the size of those loaves?

I'd be thankful for any suggestions