The way the soles come is almost a big rectangle. It is really the bowler's preference on if they put the faster or slower one in front. For me, I always have the faster sole in the front so its is more of a progressive slow down slide. The way the sole comes from Dexter, you also get to decide how much of each sole is actually on the shoe. I have soles set up that are majority the faster sole and majority the slower sole. My advice would be to cut the sole so it is big and bowl with it that way. Then fine tune from there.
I hope this helps.