by George, I think I've got it!
I find it difficult to follow a recipe whitout making a few small modification, even though I don't intend to in the beginning. This time i've increased the whole-wheat and rye flour quantity given in the formula (by ~10%), decreased the amount of bread flour, which in consequence made me increase the quantity of water. I'm pleased with the result, even if the couronne didn't expand as much as I would of wanted (I suspect it was a bit underproofed, and maybe a little underbaked??). I tried to slice the loaf after 3 hours, but it was still a bit warm in the middle, so I gave up and decided to wait until tomorrow. The crust is thick, and it shattered in pieces under the knife when I cut it.
I don't know about others, but since I bought hamelman book, my breads improved a lot. (I started baking bread about 2 years ago, having my starter since then, and I purchase hamelman's "bread" a month ago)
Recipe in romanian can be found here, translation available on the sidebar: