According to the J-CATCH tests, the F-15A was capable of detecting helicopters at 64km with its radar back in the late 1970s. The aircraft had difficulty destroying them with AIM-7E and F, but that is easily explained by the multipath issue that would be totally solved with AIM-7M. A repeat of those tests with modern high performance medium range ARH missiles is likely to show fighter aircraft are now extremely capable of countering choppers from outside the chopper’s counter-attack range.
Tangentially related is small quadrotor drones are also quite distinctive on radar, despite their significantly smaller rotor size and total size. You need to specifically tune the radar to look for them, but once you do it’s very easy to find them. Even with consumer electronics.