Size matters?

I saw a few posts where people had troubles getting higher temps. I've not had any difficulty getting up to 600+ fairly quickly. Tonight was my difficult night. Pizza again, and aiming for 600. It finally got there but took a lot longer than usual and dropped faster than usual when closing vents down.

I even cleaned out the ash area tonight before starting.

The only thing I know that was different about tonight was I reached the bottom of the bag of lump and all the pieces were tiny. Not one larger or even medium sized piece left. So is there another explanation or does the tiny pieces cover the bottom grate so much that too little air flow gets through?