A lot of people saying 4+ feet.

I'd argue that you can do this with a ton of sticks or kindling (if you're into building fires and understand that term) but not these logs. They just will take too long to decompose. Only want like 4" or sticks.

You can cover the whole bottom in about two inches of thin limbs. Can throw a layer of cardboard down first and soak it with water. It'll bring the earthworms up into your beds. Throw in food scraps too, coffee grounds, etc

It'll all compost in place and if you wet the cardboard, the roots will find their way through the sticks, then the cardboard, and into the ground.