|My DS#1 was an explosive pooper from about a week until he started solids. Although I can't say that poop never got onto the cover with the OS, it wasn't every diaper by any means (and he pooped amazing quantities, every feed, for at least the first four months or more), maybe once or twice a week. With my DS#2 it was a different story. I had him in disposables because he was a preemie, but they kept leaking when he'd pee, so at 6.5 lbs I put him in the OS, and no more leaks.
Although I have not used prefolds so cannot really compare, I can say that your OS, although likely bigger than a prefold, should work quite well at containing those explosions.