Detection and tracking at this level isn't consistent, make it too small and the radar might just see the right target at the wrong time for the pilot.
Usually they just take shotguns.
Theoretically you could teach this missile to ignore the rearmost target anyway and if I have two targets maintaining distance and velocity well... What about the cable?
A towed decoy is not meant to be seen on radar, it's meant to be seen as an EM source for radars and missiles to take their cue from, while the aircraft remains passive and stealthy and hidden within the EM background. If you want to increase RCS, then you have chaff for that, or an expendable decoy like the Britecloud.
The decoy isn't going to drag any cable along once its detached, it works both ways.