>>12394260It's likely that in a hot war against another major power a lot of engagements are likely to be settled in BVR.
For close-in fighting though all the dummy canopy needs to do is confuse the other pilot as to the orientation of the Hornet; it could cause the other pilot to correct his course in a different direction by mistake (for example he might think the Hornet will pull up in the direction of the canopy and can look pretty convincing at a distance.
Even if he manages to figure out the false canopy, that's a number of precious seconds wasted processing that idea supposedly.
The only time you'll ever really see it useful is in a really tight dogfight which would be pretty rare, but it's not like it's a whole lot of extra effort just to paint on a false canopy. It's especially effective with the F-18 because it's pretty symmetrical around the cockpit area on the top and bottom.