This image shows the on and off axis resonse of the U99.  You can see that the the high end is actually much greater on the back of the back (when in cardiod mode).  The response is flattest in the front of the mic, but thre is still a noticeable bump at 10Khz.

This is one of the most interesting features of this mic.  As you can see, in omni (green) the mic has a strong 4K dip but a strong 12K peak however, this effect reverses as you get closer to figure 8.

This is the mammoth proximity effect I was speaking of.  Vocals too thin?  Not anymore.  Just move them closer.  This graph shows the effect of being 3 cm away from the mic.  I think that's about an inch.  It's unreal how effective the proximity effect is with this mic.  So if you need more low end, move the mic forward.