I hoped it would be clear by now. So let me explain the basics. It is really not rocket science on the level to which we go here:
How does normal radar work?
The radar signal is emitted from the radar and thrown back from the aircraft. Of all the received radar signals only a small part is reflected to the sender, most waves are scattered in all directions. For the radar to be reflected to the radar sender, several conditions must be met: only the aircraft surface, that is positioned perpendicularly to the incoming radar waves does reflect them back into the same direction, from where they came from. For short moments this can be a whole wing, but most of the times the strongest echos are received from curved edges. E.g. wing leading or trailing edges. Also Propellers (or fans) are very bad because all its edges are perpendicularly many times per second. Carefully note, that even here radar waves are mostly scattered around, which means nothing else, that they are reflected in a not useful directions (where the radar receiver is not located). Still all the edges create a sufficiently large radar cross section. If surfaces stand orthogonal vs each other, the geometry acts as radar reflector with a significantly increased radar cross section.
How does stealth work?
Mostly by using an aircraft geometry, where the frame is shaped and the edges are designed carefully in a way, that the RF reflections back to the sender are minimized. Nearly all incoming radar energy (that is not absorbed by RAM) is scattered (= reflected, but not in the direction, from where it came from).
How does a signature enhancer work?
By not scattering the radar in all directions, but by reflecting each incoming RF wave exactly back to its origin. More than anything else, it primarily controls the direction of the responding emission, not its strength. The cross section of the luneburg lens is basically added to the RCS of the plane. If the plane has an RCS of 0.00143m^2, a Luneburg lens of 0.3m diameter adds an RCS of 0.0706m^2 (the area of the circle).
How does the passive radar work?
As the sender is located somewhere else, it works in principle with scattered RF only. It is basically the anti pattern, of how normal radar works. Normally a radar receives what is thrown back in its direction. Exactly the opposite happens with passive radar: the portion, that is exactly thrown back is useless for it. It has to work with the rest (and, of course, not the whole energy is scattered in the direction where the passive radar sits). But, on the other hand, it works with a large number of emitters.Classic aircraft vs classic radar, passive radar
So a classic aircraft scatters a lot of RF around and reflects sufficient amount of RF back to the radar station. The passive radar also receives a lot of input from many senders.Stealth aircraft vs classic radar, passive radar
A stealth aircraft scatters still a lot of RF around but reflects nearly nothing back in the direction, where it came from. The passive radar still receives many signals.Stealth aircraft with signature enhancer vs classic radar, passive radar
A stealth aircraft with signature enhancer scatters also a lot around, reflects nearly nothing from itself but a notable amount of RF from the enhancer back to the sender. So the passive radar does not receive a stronger signature at all (as many seem to expect due to the enhancer), but in theory even weaker signal (because some portion of the aircraft surface is covered by the Luneburg lenses, which don't scatter received RF but direct it back to the sender (which is per definition located somewhere else, than the passive radar receiver)).
The echo enhancer only works on energy passing into its aperture. That is small (but sufficient, as its echo attenuation works on distance^2 and not distance^4 attenuation that the regular scan return shows.
Echo attenuation is more something I heard in relation to rain clouds in between radar and target. So what is the distance, you mentioned?