The idea here is that you create even moisture throughout the entire curd mass and later the wheel by keeping curds small... it encourages a fast whey-off. And then after some of the moisture is lost, you lock in the rest of it by cooking fast and forming a casein shell around all the curd bits. This will let the curds finish draining in the mold, create enough tension for openings, and let the moisture mellow out during aging.
if you cut too big, what happens is that:
- Curds will retain quite a bit of moisture due to size
- When you get to the cook, casein shell will form, but curds will be rather wobbly... too much moisture inside, and very dry on outside
- With bigger curds, harder to achieve good openings because the curd insides will spill out and re-fuse once in the mold
That said, 6 mm is just a suggestion. If you feel like you want to go bigger, please do. Keep in mind all of these little details. It's a different way to make blue than what you usually find out there in recipes because you drain fast, cook fast, and actually want a carefully controlled gradient to take place. Coupled with a large floc, it should also slow down the drain. This is a very delicate, rather technical make, but try it on a small batch to see what I mean. When done right, it creates a sublime blue.