Step since that piping is shorter than the charge piping and the turbos would have the capacity to suck the uncompressed air at a faster rate than it would push it thru the charge piping in a compressed state. Also, there's more volume in the longer charge piping (and intercoolers) to fill, so it seems the charge piping is playing catch-up while the induction piping is still at max capacity. I could be way off..but this just seems logical from my layman's perspective.