【有“S型进气道”的歼-10C是拉皮隐身机?-哔哩哔哩】
Yankeesama and Shilao confirms something pretty interesting — J-10 series has an S-duct despite stealth not being a design requirement. This is because it has belly intake and since the landing gear bays gets in the way, the inlet has to twist around them and hide the engine blades. This helps the J-10C, which also applies RAM to critical areas, reduce frontal RCS significantly and it is very hard to detect when flying in formation with YY-20 or H-6. While not an actual stealth fighter by any stretch of the imagination, it is probably one of the best of its class among the 4.5th gen fighters.
Other RCS reducing measures I can think of are canted mount for radar and film treatment canopy. Since intake and radar/radome/canopy account for like 90 percent of the frontal RCS you really can achieve semi-stealth effects under clean configuration.