I read some research that analyzes the hardness of SAT solving in the average case. In fact, for a 3CNF formula if you compute the ratio of clause to variables there is an interval (more or less between 4 and 5) in which solving the formula is hard. But it is easy (between 0 and 4) high probability of satisfiable assignment and high probability of unsatisfiable assignment after ratio 5.
My question is, what about a generic formula that is not in normal form. We can say something about its hardness?