*edit* as it's currently setup the buffalo manages a decently respectable 7:1.65 on the ring but I see what you mean.
Yeah, that'd be because the FR car like that has a balance of about 56/45 ish. The MR cars on the other hand have a ratio closer to 30/70, which, for a 1000kg car, means only about 300kg on the front, and going over a crest... I needn't link to some of my favourite UFO (Unintentional Flying Object) videos

With better downforce spec on the front the MR cars are easily good for 6:52 (or better, I haven't really looked into it all that much), and the F-AWD cars can manage a 6:53 too, depending on the body.
Interesting that your car doesn't do better with CF quality 0, that's the lightest setting with medium rigidity. Normally upping the quality ups rigidity which improves sport feel but actually generally makes the time worse, though again, haven't properly looked into that! Should do a comparative tune sometime because you'd think better chassis rigidity = better road holding... or does it...