Your insurance rate is based on your yield history. Your insured rate is also discounted for late planting as well.
Now if you plant enough single crop beans to keep your yield up you may be able to to have a 45 bushel proven yield average. Then insure at the 85% level to be garantted 40 bushel. But the 20 bushel yields will drag your yield down for following years.
You won't have that 40 bushel insurance level very long with the 20 bushel harvest.
Remember you can be spot checked to make sure your yield history is correct. And if you collect more than $200,000 on any one crop it is an automatic audit of your history and yields.