You don't need to be an aerospace engineer, just understanding some very basic principles about RCS optimization is sufficient:
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One of the most important principles is to reduce the number of unaligned surfaces. Take a look at each strake and the V-tail on the opposite side - you'll see that they're parallel. There's a lot more to this, like the intakes, sides of the plane, and even a tangent line on the lower canopy are all parallel. The reflections from an EM emission source like a radar are all moving in the same direction, away from the radar.
You'll see this sort of "parallelism" everywhere. In fact, I just noticed that the side facets of the ETOS window under the J-20's nose are also parallel to the features I discussed. It's a very tight requirement for a VLO design, and removing the strakes exposes the cylindrical nozzles. A side-view cylinder is just about the worst thing you can present since a radar looking at it from any angle has a tangential plane on the surface reflecting back.
The take away is it's not the number of surfaces that's the issue, it's the number of
unaligned surfaces.