optimizing recipe(s); where best to add some ferment time to open-up top/bottom crumb?

Hi,

I have a question about where to best add fermentation time in a recipe that's "suffered" after a x-country move.

I've recently switched

    Starter microbes (mv'd x-country)
    Starter feed flour ( ~70%-extracted -> 100%-extracted organic pubpernickel/whole rye)
    Water source (filtered tap -> spring)
    Flours ( from KA organics -> Anson Mills landrace )

I've finally managed to put almost all of my build/bake problems to rest, and can once again get reliably healthy bakes.

I'm now starting the process of (re)twaking my recipes.

For, e.g., a recent loaf,

note the crumb's a bit tight @ top & bottom.
My 1st/best bet is probly to add a bit of ferment time.

That loaf was built

  build levain preferment, 4 hrs total, to domed 2x rise
  1 hr autolyse
  add levain
  15 min rest
  slap-n-fold knead, + lamination fold
  @30 mins intervals, 4x letter folds
  2 hrs add'l BF
  preshape, 1 hr rest
  shape -> banneton, 1 hr rest

then

  banneton -> retard/fridge, 15 hrs
  bake

If I want to add some ferment time to open that top/bottom crumb, where's the right, most effective place to add it?

To the levain itself?  extending out the fold intervals? in resting BF? after preshape? or in the bannetons?

I'd guess the 'when' makes a difference -- looking for some experience/guidance with where best?

thanks!

rb