Air Defence 1.01 continues…
Flying at 30ft isn’t going to save you, neither is hiding behind a tree line (unless you land as you have to come out eventually!). A modern look down-shoot down multimode pulse Doppler radar will detect and then support a missile to target even at 30ft. The modern air to air missile is going to come down from above, so your so-called ‘hiding’ at 30ft just won’t work.
There is an old story called Occam’s Razor, which applies to your hair brained idea. There are lots of folks that are subject matter experts on air defence that look for an advantage in the next air to air war, if your idea was goer then we would have seen it already. There are so many flaws in your plan of using an Extra 300 or crop spraying aircraft that I simply run out of the energy to point them all out (much of which has been said already). If it were so obvious then every Air Force would be fielding cheap aircraft to outfox their adversaries - oddly enough they aren’t!