Zooming up on Evan's pic, it looks like that front section is actually 2 C channels welded together on the flanges to form the box. The inner channel with the swoosh appears to overlap the vertical weld on the web by a bit and serves to reinforce that. They probably did that to make it a bit easier to form the pieces, longer ones being more difficult to form with the arches in the frame overall. Probably makes sense, and they likely did some stress analysis on it and decided it was OK for the application.
