Just to quote some of the key parts of Miller’s proposal:
There is no doubt that these three steps, each one supported by classic Darwinian mechanisms, would have been sufficient to fashion a rudimentary clotting system. This would leave us with system in which circulating plasma contains both an inactive serine protease and its fibrinogen target. The protease would activated by contact with tissue factor, and the active protease, in turn, would cleave sensitive sites in fibrinogen to form a clot. This system wouldn’t be nearly as quick, as responsive, or as sensitive as the current system of vertebrate clotting, but it would work a little better than the system that preceeded it, and that’s all that evolution requires.
And right here:
In short, the key to understanding the evolution of blood clotting is to appreciate that the current system did not evolve all at once. Like all biochemical systems, it evolved from genes and proteins that originally served different purposes. The powerful opportunistic pressures of natural selection progressively recruited one gene duplication after another, gradually fashioning a system in which high efficiences of controlled blood clotting made the modern vertebrate circulatory system possible.
And
Now, it would not be fair, just because we have presented a realistic evolutionary scheme, supported by gene sequences from modern organisms, to suggest that we now know exactly how the clotting system has evolved. That would be making far too much of our limited ability to reconstruct the details of the past. But nonetheless, there is little doubt that we do know enough to develop a plausible and scientifically valid scenario for how it might have evolved. And that scenario makes specific predictions that can be tested and verified against the evidence.
It is plausible mechanism that Miller proposes, and it decomposes an IC system into a serious of reducible and independent steps. Behe does not address this in any way in his book. He just ignores it.