Hi, Jim, Your loaf looks good! How does it taste? Your starter looked very happy!
I also find the larger loaf to proof more slowly than when I tested it as a smaller loaf. Ambient temperature makes a difference. I’m finding it takes 4 hours when proofed at 75-78dF, and an hour longer when proofed at 66dF. You can retard in the fridge and finish proofing in the morning if that schedule works better for you.