Maximum diameter of wood for hugels

Today a local arborist dropped off the wood I'm planning on using to build my first two hugels (urban lot, so we didn't have any of our own logs available). My housemate's convinced the logs are too big to decompose. What we have are mostly wedge-shaped pieces of a tree trunk that looks like it was about 3' in diameter. So the logs are triangular, about 1.5' deep and 6" to 1' thick on the wide side of the wedge. Too big? I think they're fine, the only problem is that a few of them are too big for me to pick up by myself.

One bed I made was from logs 2 - 3 feet in diameter, each 12 feet long, Basswood I think. The tree had split in to 3 branches at the ground, was close to the cabin and my father cut them all off at about 15ft above ground. He then put a platform and water tank on top of all 3.
When I got there they had been dead for 20 years or so. I cut them down at ground level and used the logs whole. They were decomposing pretty well already but still good enough to stay intact while I dragged them down a hill and winched them into the 2ft deep depression I dug out.
I could barely budge them at all by hand even to roll them, hundreds of pounds each for sure.

I'm sure your cut up logs will be fine. If you can pick up one end and flip them over, you can get them there eventually. Once you bury them they'll rot quickly and last a long time