On historical scenario there are subsonic targets (E-2, E-3 etc.)
Also it is important to note that the closer velocity (radial speed) is important, not the target's own speed.

As I am unable to switch on my SAMSIM computer, try this - do a mission with IADS (Ashuluk), then pick up the target's speed value from the AAR. Than restart the SIM and do same mission manually, so you could input the radial speed manually. Please do a photo of the velocity indicator, but only the upper part (S or D key if I remember correctly). Try circle scan...