question about ad9625

I have a question about ad9625.It runs well  when I configure ad9625 for full bandwidth using 8 lane (serdes rate is 5Gbps). But It does not run well when I change 8 lanes into 6 lanes for full bandwidth.What's the difference between the configuration of 8 lanes and 6 lanes. How can I change something register configurations as little as much when change from 8 lanes to 6 lanes.Thanks