Via Farm Policy I found the link to this map from Amber Waves (Mar 12) which shows the ratio between direct payments and crop insurance subsidies by county (part of a discussion of "conservation compliance", except they call it "environmental compliance", tying government benefits to the swampbuster/sodbuster provisions of the 1985 Act.
The map shows why many are pushing crop insurance, given the subsidy is higher than for direct payments, but there's some interesting variations. Oklahoma for example sticks out between Texas and Kansas. I'm not sure why, but it does.
If I understand, crop insurance could be a higher percentage of direct payments for a number of reasons. The FSA yields or acreage bases could be low or the crop insurance actuarials could be high. Or the number of crop insurance policies sold could be high. I wonder if there's existing maps of such data.