Actually, it's size is perfect for its winter mountainous terrain where it often chases it's prey on narrow ridges, ledges, and higher altitudes with less oxygen. A larger size would be too much of a drag for that environment as well as a reduction in intercept capability.
It's kinda like how a 4X4 midsize SUV or Jeep fairs better than a full size 4X4 SUV in certain off road conditions where more width and weight becomes a burden.