I've read many times over the years that the chines being cut back on
the YF-12A reduced the directionaly stability of the Blackbird to the
point that it required the three ventrals. To me that doesn't seem to
make sense since the chines are oriented in the horizontal plane.
However the YF-12A has that large radome upfront which adds side area
to the nose which would decrease directional stability. Which is it?

Thanks.