To clarify what I mean, imagine the case of a 1D automaton with cells C1, C2, C3. If I run the standard propagation model with C1 initially infected, what happens is that C1 may infect C2, and then when C2 gets infected, it may infect C3. By running this 100 times, I can get an estimate of the probability at every iteration that C2 or C3 are infected.
If I try to propagate probability directly, what happens is that I have initial probability p2(C1) = 1, p2(C2) = 0, p2(C3) = 0.