Or is it that they do not allow the IGV, compressor blades to be visible ?
Stand in front of the intake on an older non-stealthy jet fighter or attack aircraft and the IGV, compressor
blades are quite visible from outside the inlet.
I would be careful just adding blockers inside the inlet.
For one, the blockers not only block E-M waves but also the airflow to the engine.
On the F-117 they may have sized the inlet to compensate for the mesh blocker area
obstruction. In other words the inlet is larger than it normally would need to be
without blockers inserted.
For a subsonic F-117A that also will never have to diffuse the supersonic airflow
down to subsonic and also doesn't have an afterburner this would be OK.
For a F-22 or F-35 or lower RCS F-15 where the aircraft can fly well into supersonic
and thus has a supersonic inlet diffuser that needs to use shock waves to slow the air down
to subsonic and also has to handle moving the normal shock around in potential inlet unstarts,
and has a much wider performance range than the F-117A, adding obstructions to the inlet
doesn't sound like a good idea to me.
But I am not a stealth technology enthusiast at the moment. I prefer to spend my time on
hypersonic topics. Someday I'll get more into stealth. But the above would be my concerns
coming from just a airbreathing inlet technology standpoint.
