I like the way you are describing your shipping method!My cost is $35 per dozen. I put peanuts in the bottom then line with bubble wrap. I wrap each egg individually in bubble wrap pouches and lay them in the box. When done, I fill with peanuts until there is just enough room to close the box. I've had good luck shipping this way and people have had good hatch rates.
I think some times the eggs are packed in so tightly they are not allowed to shift at all in the box so any concussive force travels through the egg to the embryo so the egg shell is intact on delivery, but the embryo not so much. I like the packing to take a little of the shock. Sort of like having springs vs a hard board to sit on when you travel on a bumpy road. I'll take the springy seat and not get my teeth jarred, thank you very much!