"Another good reason not to open up the Ostie indiscriminately, is it spotlights your location."
I've noticed that, if you have tracers turned off, the M16's bullet stream is invisible, which may or may not be handy if you want to sneak about. I assume the 37mm rounds fired from the Ostwind (and the Yak9T) remain visible, even with tracers off, because they are combined high explosive tracers, although I could be very wrong.