The rendering of InSight shows the RISE antennas, the two microwave horns pointed just above the horizontal over each of the solar array paddles.
If I understand correctly the experiment works when signals from these horns are received on Earth when Mars' rotation puts InSight on the edge of the planet as seen from Earth, maximizing the Doppler shift and its sensitivity to changes in planet rotation.
According to this answer and the linked source there:
...it's job is to stay on the lander deck and trade X-band radio signals back and forth with Earth for an hour or so each day.
That suggests there is some significant directionality of the antennas, perhaps 15 degrees, which is consistent with the apparent aperture shown in the image considering the X-band wavelength will be about 3.5 cm (I'm guessing about 8.6 GHz).
This works if the antennas point roughly East/West (really, in the plane of the ecliptic) and would probably be hopeless if they ended up pointing North/South.
From this short conference paper:
For RISE, Doppler measurements will be made at times when the Earth is at low elevation, when the Doppler signature due to the rotation of Mars is largest. Two fixed medium-gain antennas, one pointed to the east and one pointed to the west, will be used to provide adequate gain for RISE.
Question: How will InSight's RISE antennas end up pointed in the right direction?
Related to the RISE instrument and its operation:
- How will “InSight's onboard communications gear perform a radio-science experiment to shed further light on Mars' innards?” (Space.com)
- How many solar system bodies have had coherent radio transponders?
"The Mars InSight lander as depicted in an illustration with its instruments deployed on the surface of Mars. Image: NASA/JPL-Caltech" Cropped from Source