If such an aircraft with towed banner is made, make sure to add these lines (or swap them) in the aircraft's data.INI file:
[DetectSystem]
RadarType=
VisualBlindArc=1,2,3,4,5,6,7,8,9,10,11
VisualRestrictedArc=1L,2L,3L,4L,5L,6L,7L,8L,9L,10L,11L,12L,1H,2H,3H,4H,5H,6H,7H,8H,9H,10H,11H,12H
MaxVisibleDistance=6000.0
HasRWR=FALSE
That will give the "enemy pilot" only a line of sight strait to the front. Otherwise, when you try to engage the banner, the AI aircraft will start to evade, or try to move itself in firing position.