After personal experience and various readings from books and other soapers, I think that cracks on top of soap paste in the mold is taking place also because of the partial gel phenomenon.
I always CPOP all my soaps, even those with milk and beer in which I always add table sugar, without having any problems.
So my theory is that at partial gel, only the inner side of soap melts and becomes soft while the outer side is still hard without elasticity, and that difference makes the cracking on top, even the volcano if the heat is more intense in the inside.
So I think forcing full gel is a must besides the aesthetic (coloring) issues.